(ETC)

Certified Program for Electrical Engineers "Building Installation"

Part (2)Lighting

1. Lighting Terms

In artificial lighting, many technical terms and units are used to describe and illustrate the properties of light sources and the effects that are produced.

1.1. Luminous FluxLuminous flux describes the total amount of light emitted by a light source. This flux is measured in Lumen (lm).

1.2. Luminous efficacyLuminous efficacy describes the luminous flux of a lamp in relation to its power consumption and is therefore expressed in lumen per watt (lm/W).

1.3. Luminous intensityAn ideal point-source lamp radiates luminous flux uniformly into the space in all directions; its luminous intensity is the same in all directions. In practice, however, luminous flux is not distributed uniformly. This results partly from the design of the light source, and partly on the way the light is intentionally directed. It makes sense, therefore, to have a way of presenting the spatial distribution of luminous flux, i.e. the luminous intensity dis tribution of the light source. The unit for measuring luminous intensity is candela (cd). The candela is the primary basic unit in lighting technology from which all others are derived. The candela was originally defined by the luminous intensity of a standardized candle. Later thorium powder at the temperature of the solidification of platinum was de- fined as the standard; since 1979 the candelahas been defined by a source of radiation that radiates 1/683 W per steradian at a frequency of 540 1012 Hz.

1.4. IlluminanceIt indicates the amount of luminous flux from a light source falling on a given area.

Average illuminance Em is calculated from the Horizontal illuminance Eh and vertical illuminnance Ev in interior spaces are relative to the location of the calculation surface within a room.

The illuminance at a point Ep is calculated from the luminous intensity l and the distance a between the light source and the given point

1.5. Luminance

Whereas illuminance indicates the amount of luminous flux falling on a given surface, luminance describes the brightness of an illuminated or luminous surface. Luminance is defined as the ratio of luminous intensity of a surface (cd) to the projected area of this surface (m2).

The luminance of a luminous surface is the ratio of luminous intensity l and the projected surface area Ap.

The luminance of an illuminated surface with diffuse reflectance is proportional to the illuminance and the reflectance of the surface.

1.6. ReflectanceAs might be expected, there is a relationship between the amount of light incident on a surface and the amount of light reflected from the same surface. The simplest form of the relationship is quantified by the luminance coefficient. The luminance coefficient is the ratio of the luminance of the surface to the illuminance incident on the surface and has units of candela/lumen. The luminance coefficient of a given surface is dependent on the nature of the surface and the geometry between the lighting, surface and observer.

The following table illustrates the photometric quantities with their related units:MeasureDefinitionUnits

Luminous fluxThat quantity of radiant flux which expresses its capacity to produce visual sensationlumens (lm)

Luminous intensityThe luminous flux emitted in a very narrow cone containing the given direction divided by the solid angle of the cone, i.e. luminous flux/unit solid angle.candela (cd)

IlluminanceThe luminous flux/unit area at a point ona surfacelumen/m2

LuminanceThe luminous flux emitted in a givendirection divided by the product of the projected area of the source element perpendicular to the direction and the solid angle containing that direction, i.e. luminous intensity/unit areacandela/m2

ReflectanceThe ratio of the luminous flux reflected from surface to the luminous flux incident on it

2. Lighting Characteristics2.1. Color temperature

Given that the color of the light has an important influence on the color impression of the area, the color temperature of the light source plays an essential role. To enable an objective comparison of the color impressions from various sources, subjective terms such as the popular words cool and warm are inadequate. A precise scale is required and given by the term correlated color temperature; the color gradation of the light is compared with the light emitted by an intensely heated iron bar of which the temperature is known. In this way, the light color can be specified by a value in Kelvin (K). A low color temperature represents warm, yellow, orange or red light and a high color temperature cool, blue or violet light.

Four categories, as a practical guideline, are:

2.1.1. (2500 - 2800 K warm/cosy)The color from incandescent lamps, (compact) fluorescent lamps in the colors 827 and 927 and the SDW-T White SON lamp. Generally used for intimate and cosy environments where the emphasis is on a peaceful relaxing ambience.

2.1.2. (2800 - 3000 K warm/neutral)The color from halogen lamps, color 830 and 930 (compact) fluorescent lamps and MASTERColour 830 lamps. Used in places where people are active, requiring a welcoming comfortable ambience.

2.1.3. (3000 - 5000 K neutral/cool)The light color from 840 and 940 fluorescent lamps as well as MASTERColour 942 and MHN metal halide lamps. Usually applied in commercial areas and offices where a look of cool efficiency is desired.

2.1.4. (5000 K and above daylight and cool daylight)The light color that best matches natural daylight, such as fluorescent colors 850, 865, 950 and 965 and the new ActiViva colors 451 and 452.

2.2. Color rendering

The perception of surface colors, the color rendering of the light, depends on the color content of the incident light. The light emitted by a light source is composed of a mixture of colors, all in different intensities. A change in the color mixture and intensity yields a different color rendering. Cool daylight and incandescent lamps have fully natural color rendering properties. The same is true for halogen lamps. The reason for this is the continuous spectrum of the sources, which is typical for filament lamps. Most gas discharge sources, however, have an interrupted or line spect rum. This has an influence on the quality of their color rendering properties, which vary from very poor, with sodium gas discharge lamps, to excellent, with the color 90 De Luxe series fluorescent and MASTERColour 942 lamps. When selecting a particular lamp type, a clear understanding of the color rendering properties is essential. A fair indication is given by the color rendering index (CRI), which is a standardized scale with 100 as the maximum value. Colors are best shown under a light source with the highest color rendering index. Incidentally, it is only worthwhile to compare CRI values of lamps of similar color temperature. In practice, three color rendering categories are normally found. CRI between Ra 90 and 100. Excellent color rendering properties. Applications are mainly those where correct color appraisal is a critical task. CRI between Ra 80 and 90. Good color rendering properties. Applications in areas where critical color appraisal is not the primary consideration but where good rendition of colors is essential. CRI below Ra 80. Moderate to poor color rendering properties. Applications in areas where the quality of color rendering is of minor importance. The choice in favor of a particular color rendering class does, of course, depend on the demands that an application makes on a lamp. For example, a CRI of Ra 60 is inadequate for shop lighting, but is qualified as good for functional road lighting. 2.2.1. Areas of application

Correct light impressions and correct rendering of colors assists us in recognizing our surroundings. The color climate of an artificially-lit space is determined by light color temperature and color rendering. Room furnishings of wood and fabrics in warm colors require warm lighting in the colors 827 or 927. For pleasing light the colors 830 and 930 are most suitable for many applications. The more business-like the interiors are, the cooler the light can be. Furniture using chromium, glass and marble, or in black and white, is emphasized by the neutral light colors 840 and 940. Colors 865 and 965 are best used in environments where there is a high daylight content. For (compact) fluorescent lamps it is most economical to choose the colors 830 and 840 as they produce the highest light output. Colors 927, 930, 940 and 950, on the other hand, give the best color rendering.

3. Electric light 3.1. Incandescent The incandescent lamp is operated by heating a filament in the lamp to a high temperature, so that it emits light. The basic principle of the lamp may be simple but the technology required to maintain a filament at a high enough temperature to give significant amount of light whilst ensuring the lamp has a reasonable life is highly complex. The basic and most popular form of the lamp is the General Lighting Service (GLS) lamp. The filament design is critical in setting up the operating characteristics of the lamp. The length of the filament wire is largely determined by the supply voltage, whilst the thickness of the wire is determined by the operating current of the lamp. The filament is coiled to reduce heat convection to the filling gas. There are various forms of filament coiling with the coiled coil being one of the most common.The filament must be robust enough to withstand the shocks and vibration that the lamp receives during its life and at the same time be rigid enough so that it does not droop. Support wires can help prevent the filament from drooping but they conduct heat away from the filament and thus reduce the efficiency of the lamp. Therefore normal service lamps are made with hard brittle filaments that only need a few support wires. Lamps for rough service are made with a softer more malleable filament but have several support wires. The bulb is generally made of a soft soda glass and its size is set so that it does not get too hot and the tungsten that evaporates from the filament during the life of the lamp does not blacken the bulb too much. The gas filling of the lamp is present to reduce the rate at which the tungsten evaporates and thus make the lamp last longer. To minimize the heat losses from the filament noble gasses are used as the primary fill gases. Most lamps have argon based filling but some high performance lamps use krypton. In addition to the noble gas filling most mains voltage lamps have a small percentage of nitrogen added to the filling to help suppress arcing at the end of life. There are many variations on this basic lamp type. They are designed to run on voltages between 1.5 and 415 volts at wattages between 1 and 1,000 watts. There is also a wide variety of bulb shapes including lamps with built in reflectors.

3.2. Tungsten halogen The applications of conventional incandescent lamps are limited by their physical size and luminous efficiency. Raising the filament temperature to increase the luminous output has the effect of increasing the rate of blackening of the glass envelope, blackening which is a result of the evaporation of tungsten from the filament. By adding a halogen to the gas fill a chemical transport cycle involving the reaction of tungsten reduces the amount of blackening of the envelope. It is then possible to reduce the size of lamp, increase the pressure of the filling gas and thereby limit the loss of the tungsten from the filament.

The chemistry of the tungsten halogen cycle is highly complex. However the key stages are: the halogen combining with the tungsten on the wall of the lamp (zone 3) the tungsten halide vapor mixing with the fill gas of the lamp (zone 2) the tungsten halide dissociating close to the filament of the lamp, leaving the halogen free to migrate though the fill gas to the lamp wall again and the tungsten being deposited on the filament (zone 1). To enable an efficient cycle it is necessary for the wall of the lamp to run at a temperature above 250 C; this means that the bulb has to be made from quartz or hard glass. Tungsten halogen lamps are more efficient and have longer lives compared with standard tungsten lamps. Also they are more compact than standard lamps. However they are more expensive as it is hard to make the quartz outer bulb and it is harder to introduce the gas fill into the lamp due to the high filling pressure. 3.3. FluorescentFluorescent lamps are the most commonly used form of discharge lamp. They come in a variety of shapes and sizes and are available in a wide range of colors. The original form of the lamp was a long straight tube. New forms of the lamp known as compact fluorescent lamps have been developed where the lamp tube is bent or folded to produce a smaller light source. Fluorescent lamps work by generating ultraviolet radiation in a discharge in low pressure mercury vapor. This is then converted into visible light by a phosphor coating on the inside of the tube. The electric current supplied to the discharge has to be limited by control gear to maintain stable operation of the lamp. Traditionally this is done with magnetic chokes but most circuits now use high frequency electronic control gear. Electronic control gear has a number of advantages: first, driving the lamp at high frequency maintains the ions in the gas and thus makes the lamp run more efficiently. Secondly, it reduces the amount of flicker in the lamp and, finally, electronic gear consumes less power than a magnetic choke.

The lamps are made from the following main components. The tube: this is made from a glass with a high iron content so that any short wave UV radiation that gets through the phosphor coating is absorbed by the glass The phosphor coating: there are a wide variety of phosphors available. Each produces a different spectrum of light and by careful blending of the various phosphors lamp makers can tailor a wide range of lamp colors. The lumen output of the lamp also depends on the choice of phosphor mix. It is also important to control the particle size of the phosphor powders and the thickness of the coating. There are three main types of phosphor mixes currently used in fluorescent lamps: Halophosphates: this range of phosphors tend to emit light in a relatively wide band and it is normal to use only one phosphor of this type at any one time. Halophosphates are only reasonably efficient as phosphors and generally have poor color rendering. Tri-phosphors: are mixes of three narrow band phosphors. They generally achieve CIE general color rendering indices greater than 80 and have a high efficacy and good lumen maintenance. Multi-phosphors: are mixes of a number, usually five, phosphors. These mixes usually give a CIE general color rending index higher than 90, however the efficacy is normally lower than a tri-phosphor mix. The electrodes: generally coils of tungsten wire that are coated in a material that when heated will give off electrons readily. To start the lamp a current is passed through the coil to heat the emissive coating. However, once the lamp is running the ionized gas atoms hitting the electrode provide enough energy to keep the cathode hot. The electrodes are generally surrounded by a shield as some of the material used to coat the electrode evaporates during the life of the lamp. If the shield was not there the material would be deposited on the wall of the lamp causing a black ring and reducing the light output. The gas fill: the lamp fill is made up of two components; a noble gas mixture and the mercury vapor. The noble gas in the lamp has three main functions. First, it reduces the mobility of the free electrons in the lamp and by careful control of the pressure; it optimizes the number of electrons with the right amount of energy to excite the mercury atoms. Secondly, the gas reduces the rate at which the coatings on the electrodes evaporate and thus prolongs the life of the lamp. Finally it lowers the breakdown voltage of the lamp and thus makes starting easier. Most lamps use either a mixture of argon and krypton or neon and argon. The use of the heaver krypton gas makes the lamps slightly more efficient but it is significantly more expensive. The vapor pressure of mercury in the lamp is significantly lower than the pressure of the noble gas mixture and it is controlled by the temperature of the coolest part of the lamp. At the cold spot of the lamp the mercury condenses to form liquid mercury. At this point the liquid and gaseous mercury are in equilibrium and the vapor pressure is determined by the temperature. As the vapor pressure of mercury is critical to the operation of the lamp, the light output of the lamp varies with temperature. Most lamps are optimized to run in an environment with an ambient temperature of 25 C. However, some of the new types of lamp are set up to run in an ambient temperature of 35 C. In some lamp types the mercury dose is mixed with other metals such as bismuth or indium. These metals form an amalgam with the mercury and this reduces the vapor pressure of the mercury at any given temperature. This enables the lamp to operate at higher temperatures but has the drawback that the lamp takes a long time to reach full output.

There are two main types of fluorescent lamps; the traditional linear lamps and the compact fluorescent lamps. Linear lamps come in variety of diameters and lengths. The main diameters of lamp are the T12 lamps which are 38 mm in diameter, T8 lamps which are 25 mm and the T5 types which are 16 mm. All of these families of lamps come in a variety of lengths and wattages. Linear fluorescent lamps are generally efficient light sources with some of the lamps approaching 100 lumens per watt. They also come in a wide variety of colours with a range of colour rendering properties. Table 3.3 gives a summary of the main lamp colours.

In general compact fluorescent lamps are less efficient than linear lamps, but because of their small size, they are suited to many applications where a smaller lamp is needed. Some of the lamps have the control gear built into them and can be retro-fitted into GLS lamp sockets.3.4 High pressure mercuryIn this type of lamp a discharge takes place in a quartz discharge tube containing mercury vapor at high pressure (2 to 10 atmospheres). Some of the radiation from the discharge occurs in the visible spectrum but part of the radiation is emitted in the ultraviolet. The outer bulb of the lamp is coated internally with a phosphor that converts this UV radiation into light. The general construction of the lamp is shown in the figure.The operation of the lamp is quite complex and needs to be considered in three phases: ignition, run-up and stable running.First ignition; when power is first applied to the lamp the voltage is not high enough to strike an arc between the two main electrodes. Ignition is achieved using an auxiliary electrode placed close to one of the main electrodes. The auxiliary electrode is connected via a resistor (typically 25,000 ohms). This limits the size of the current in the arc formed by the auxiliary electrode so the voltage across the starting arc is reduced as the current increases. This means that the ions in the arc are drawn towards the main electrode at the other end of the lamp and these ions allow the main arc to start. The next stage is the run-up. Once the arc has started between the main electrodes very little light is given out because the mercury pressure is too low as the tube is cool. The arc in the gas slowly warms up the tube and so the mercury vapour pressure rises and the light output increases. Typically it takes about 4 minutes for the lamp to achieve 80% of the final light output.When the lamp reaches stable running and normal operating pressure all the mercury in the lamp is in the vapour phase. This means that the vapour pressure of the mercury is controlled by the amount of mercury put into the lamp rather than the temperature of the lamp.High pressure mercury lamps are made from the following main components.The discharge tube is generally made of quartz and has the main electrodes and the starting electrode sealed into it.The main electrodes are usually made of tungsten rods which have coil of tungsten wire wrapped round them. This coil is usually impregnated with emitter material similar to that used in fluorescent lamps. The auxiliary electrode is generally wire made out of molybdenum or tungsten.The fill gas in the discharge tube is commonly argon and a very carefully controlled dose of mercury is also added. The discharge tube is fitted into a support frame and the whole assembly is sealed into the outer bulb. The gas fill in the outer bulb is usually nitrogen or argon or a mixture of the two. The pressure of this fill gas is controlled to ensure that the arc tube operating temperature is correct.The outer bulb is made out of a soft soda lime glass for low wattage lamps (up to 125 W). High power lamps use a borosilicate glass outer. There are two common shapes for the outer bulb the ovoid or isothermal bulb, and the reflector bulb. Figure below shows these two shapes.

The performance of these lamps is not considered to be very good nowadays. Their efficiency is around 40 lumens per watt. Their CIE general color rendering index is between 40 and 50 and they have a very long life but, because of poor lumen maintenance, it is generally recommended that the lamps are changed after 8,000 to 10,000 hours of use. Because of their poor performance and the fact that better lamp types are available for almost all of the applications these lamps are being phased out.3.5 Metal halideMetal halide lamps were developed as a way of improving the performance of high pressure mercury lamps in terms of their colour appearance and light output. They work by introducing the salts of other metals into the arc tube. As each element has its own characteristic spectral line, by adding a mixture of different elements into the discharge it is possible to create a light source with good colour rendering in a variety of colours. There are a lot of problems with introducing new elements into a discharge. First, the element must be volatile and secondly it should not chemically attack the arc tube. To avoid these problems it has become common practice to introduce metals into the lamp as metal halides. Metal halides are generally more volatile than the metals themselves and the metal halides do not attack the arc tube. The metal halide compound breaks up into the metal and halogen ions at the high temperatures in the centre of the discharge and reforms at the lower temperatures near the wall of the tube. Many different combinations of elements have been used to make metal halide lamps, Figure 3.21 lists some of the more common combinations of elements together with the spectral output they create.

Because of the differing lamp chemistry there is a wide range of lamps that vary in terms of their efficacy, colour and electrical properties.One of the main problems with metal halide lamps that use quartz discharge tubes is colour stability. As the colour of the light output is a function of the ions present in the discharge tube, any changes to the gas composition due to some metals being absorbed by the quartz tube or changes in temperature in the tube can cause significant colour shifts. These colour shifts are particularly a problem for the lower wattage lamps. This problem has largely been solved by the introduction of a new material for the discharge tube. Ceramic or sintered alumina tubes are much more resistant to chemical attack than quartz tubes and can operate at higher temperatures. Lamps with these tubes are now very popular for low wattage (up to 150 W) metal halide lamps.The construction of a metal halide lamp is similar to that of a high pressure mercury lamp. The key differences are that it is unusual to use an auxiliary electrode in the lamp, lamp ignition being achieved using a high voltage pulse from the control gear. Also, there is no phosphor coating on the outer bulb.

There is a vast range of metal halide lamps ranging in power between 20 W to over 2 kW. The lamps have a CIE general colour rendering index between 60 and 93 and they have high luminous efficacies, in the range 60 to 98 lumens per watt. For these reasons, this lamp type has many applications where a compact light source with good colour rendering is needed. There are many points to watch for when selecting metal halide lamps as there are problems associated with some lamp types shattering at the end of life or giving off UV radiation. It is important with these lamps to ensure that the luminaire in which they are used is suitable. 3.6 Low pressure sodiumLow pressure sodium lamps are similar in many ways to fluorescent lamps as they are both low pressure discharge lamps. All the differences in characteristics stem from the use of sodium in the discharge tube rather than mercury. The key differences are the need to run the lamp hotter to maintain the vapour pressure of sodium, the need to contain the very reactive sodium metal; and the fact that sodium emits its light in the visible rather than the UV frequency range, so there is no need for a phosphor layer. There used to be a range of designs for sodium lamps but currently the U-tube lamp is by far the most common type. A typical lamp of this design is shown in the figure.

The main components of a low pressure sodium lamp are as follows.The arc tube; this is made of normal soda lime glass with a coating on the inside of a special sodium resistant aluminoborate glass. Making this ply-glass tube is technically difficult as great care is needed to ensure that there are no thermal stresses in the final tube that might lead to cracking during the life of the lamp. Some lamp types have dimples in the side of them to act as reservoirs of sodium. The gas fill of the tube is neon with about 1% of argon at a pressure of approximately 1000 Pa. This mixture is used as it has a much lower breakdown voltage than neon on its own and thus makes starting the lamp much easier. Sodium metal is also put into the tube. The sodium vapour pressure in the tube when it is at its operating temperature of 260 C is about 0.7 Pa. The outer bulb is of soda lime glass, the inside is coated with a layer of indium oxide. This layer reflects the bulk of the infrared radiation from the arc tube and thus keeps it warm. Between the outer bulb and the arc tube the gas pressure is very low, below 0.01 Pa. To maintain the vacuum a barium getter is used. A relatively high voltage is needed to start an arc in the neon fill gas. The arc then slowly warms up the lamp and the discharge tube and the vapour pressure of the sodium starts to rise until the lamp reaches thermal stability after about 15 minutes.One of the curious properties of the sodium atom is the predominance of the energy transitions associated with the two spectral lines at 589 nm and 589.6 nm. This means that virtually all the visible radiation from the lamp is given off in this very narrow band. However, sodium atoms will also re-absorb and re-emit the radiation very readily; this means that nearly all the light emerging from a low pressure sodium lamp has come from close to the arc tube wall. The light from a low pressure sodium lamp is a wavelength close to the peak of the photopic sensitivity curve, and as the lamp is relatively efficient at converting electricity into visible radiation, the lamp is one of the most efficient light sources in terms of lumens per watt. The best of the range can achieve in excess of 180 lumens per watt. The problems with the lamp are large size, long run-up time and monochromatic light that does not render colours. The lamp has been mainly used for street lighting but recently the importance of some colour rendering on roads has been recognized and the lamp is rarely used in new installations. 3.7 High pressure sodiumThe high pressure sodium lamp generates light in a discharge through sodium vapour at high pressure. As the vapour pressure of sodium in a lamp rises the spectrum at first broadens and then it splits in two with a gap appearing at about 586 nm. The below figure shows the spectra from sodium lamps with different vapour pressures.

As the vapour pressure rises the colour rendering of the lamp increases. However, this is at the expense of efficacy in terms of lumens per watt. The figure below shows the construction of a high pressure sodium lamp.

The main components used in the construction of the lamp are as follows. The arc tube is made of polycrystalline alumina (PCA). This material is ceramic rather than a glass, this makes it very hard to work as it is not possible to soften it and it is hard to cut. PCA is used because it is resistant to chemical attack by hot sodium, it is stable at high temperatures and it is transparent. Because it is not possible to work the PCA the tube is cut to length and fitted with end caps, the figure below shows some of the designs used for closing the ends of the discharge tube.

The use of niobium metal as part of the end cap assembly is common as it expands with temperature at the same rate as the PCA tube and thus does not cause stresses in the lamp as it heats up. The electrodes in the lamp are made from tungsten rods with tungsten wire wound around them, with emitter material made from oxides of metals such as barium, calcium and yttrium.The fill gas in the tube is usually xenon at a cold pressure of 3 kPa, which corresponds to an operating pressure of about 20 kPa. A higher xenon pressure would improve lamp efficacy but make starting harder as it needs a high voltage to break down. Some types of lamp use high pressure xenon and use an ignition wire held close to the tube to help starting. There are also some lamps that use argon as a fill gas; they are much easier to start but are less efficient in term of lumens per watt. A dose of sodium mercury amalgam is used in most high pressure sodium lamps. Mercury is used because its vapour acts as a buffer gas and helps improve the efficiency of the lamp. However, the mercury contributes very little to the output spectrum of the lamp. Some lamps are now made without mercury in them. The absence of mercury makes the disposal of the lamp at the end of life easier as there are no environmentally damaging substances in the lamp. The metal dose in the lamp is never fully vapourised and so the pressure of the sodium and mercury vapours in the lamp is dependent on the temperature of the coolest part of the discharge tube. This makes the output of the lamp temperature dependent and can also give problems associated with the voltage across the tube rising if the lamp gets too hot. The cold spot on most discharge tubes is in the area behind the electrode. As this area of the tube is blackened through the life of the lamp, the cold spot temperature tends to rise through life. This can give rise to problems in old lamps where the pressure in the discharge tube rises to the point where it is no longer possible for the voltage available from the supply to sustain an arc in the lamp. The discharge tube is mounted into a support frame and sealed into an outer bulb. The outer bulb is generally made of a borosilicate glass and may be in a number of different shapes, the figure below shows some of the more common shapes.

The high pressure sodium lamp is an efficient source of light (efficacies up to 142 lumens per watt), it has a long life with reasonable lumen maintenance and whilst the colour rendering on the standard lamp is poor it is acceptable for a number of applications. The white high pressure sodium lamp has a spectrum with minimal output in the yellow. This has the property of making a large number of colours appear more vivid and so this lamp has a number of applications in retail lighting.

3.8 InductionInduction lamps are essentially gas discharge lamps that do not have electrodes. Instead the electric field in the lamp is induced by an induction coil that is operating at high frequency. The only types of induction lamps that are currently in production are based on fluorescent lamp technology. The figure below shows the layout of a cavity type lamp.

The lamp consists of a glass bottle with a cavity in it into which the induction coil is placed. The glass vessel has a gas filling similar to a conventional fluorescent lamp and the phosphor coating on the inside of the lamp is also similar. The induction coil in the centre of the lamp is fed from a high frequency generator. An alternative architecture for this type of lamp is to have the induction coil wrapped around a toroidal lamp. The figure shows a lamp of this type.

Induction lamps have many of the same properties as fluorescent lamps. They are, however, slightly less efficient. The big advantage with this type of lamp is long life. This is because there are no electrodes to fail and the inside of lamp does not get coated with material that has been vapourised away from the electrodes. A number of lamps of this type have rated lives of 100,000 hours. These lamps are more expensive than conventional fluorescent lamps so they tend to be used in places where it is difficult to change lamps and thus long life is an important requirement. 3.9 Light emitting diodesLEDs are available in a wide variety of sizes, colours and power ratings and development is proceeding at a rapid rate. Whilst LEDs come in a variety of styles, the figure below illustrates two common forms.

The main components of a LED are as follows. The chip of semiconductor material in the centre of the lamp may be made of a wide variety of materials. Differing materials result in a different colour of light being produced. The table below lists some of the more commonly used materials.

The chip is mounted onto one of the lead in wires. In high power LEDs the mounting is designed in such a way as to conduct heat away from the chip. The other lead wire is bonded to the chip generally connecting to a very small area close to the actual semi conductor junction. The whole device is then potted in a plastic resin, usually epoxy.LEDs generally have a long life and may last up to 100,000 hours. LEDs generally emit light in a relatively narrow band so that most LEDs produce light that is a saturated colour. It is possible to make white LEDs by using a blue or ultraviolet chip and putting a phosphor coat round it. White can also be achieved by combining a mixture of red, green and blue chips. LEDs have a lot of applications associated with signals and signage. The use of saturated colours in these applications is a real bonus. This coupled with the ease of producing light in a number of small units means that LEDs are replacing a number of other light sources in these areas. It is also possible to make lamps that are a cluster of LEDs of different colours. By controlling the outputs of the different colours it is possible to make a lamp that can produce light in a wide variety of colours. At the time of writing, white LEDs are making fast technical progress but have not proved to have that many applications in the area of general lighting as the lumen packages tend to be small and their efficacy does not compare favourably with other sources such as fluorescent lamps. 4. Electric light source characteristicsThere are a number of key properties of lamps that need to be considered when choosing which lamp is right for a particular application. The following sections list these properties. 4.1 Luminous fluxIn any lighting application the amount of light that is needed is a key decision that has to be made. From this it is then possible to work out how many lamps of given rating are needed. There are lamps with lumen outputs less than 1 lumen through to lamps with outputs in excess of 200,000 lumens. In most applications, it is the average maintained illuminance that is important so it is important to consider the lumen maintenance through life at the same time as the initial luminous flux. 4.2 Power demandIt is important in any lighting scheme to know what the total power demand is going to be so that the electrical infrastructure can be correctly designed. The power consumed by the lamp is important. However with many lamp types it is important also to consider the impact of the control gear as well. In most cases it will be the total circuit watts that is important rather than the lamp wattage. One further complication with some lamp types is that the voltage and current waveforms are not exactly in phase with one another. Thus the volts multiplied by the amps in the circuit may be higher than the watts. The power factor of the circuit is defined by the following equation:

Most high wattage lamp circuits are designed to have a power factor greater than 0.85. The other factor that may affect the sizing of the cables that supply a lighting installation is the current required during the run-up of the lamps. With some types of lamp this can be over double the nominal running current. When using lighting controls the power demand is more difficult to predict as the power consumed may be reduced at times when full output is not required from the lamp.

4.3 Luminous efficacyLuminous efficacy is usually expressed in terms of lumens per watt. Many lamp manufacturers produce lumens per watt figures for their lamps. However, for discharge lamps and other lamps requiring some form of control gear, these figures may be misleading as they refer to the power consumed in the lamp only and do not consider the power lost in the control gear. All the values quoted in this chapter for efficacy are based on total circuit watts. Efficacy is a primary concern when selecting a lamp. In general, if a range of lamps suitable for a particular installation then it is the most efficient that should be used. 4.4 Lumen maintenanceThe light output of most lamps decreases as the lamps get older. With some relatively short life lamps this is not a problem as they fail before the light output has fallen significantly.3.4.5 LifeIt is normal when considering the life of a lamp to talk about the percentage of lamps that will survive after a certain number of hours of operation. This value is known as the lamp survival factor (LSF). Other factors in a particular installation may affect the life of the lamp used. These factors include the switching frequency, the supply voltage, the ambient temperature and presence of vibration.It is often the case that the combined effect of the number of lamp failures coupled with the reduced lumen output of the lamps makes it necessary to replace the lamps in an installation. Sometimes lamp makers quote an economic service life for lamps, this generally is the point where the LSF multiplied by the LLMF falls below 0.7. 4.6 Colour propertiesThe colour of the light produced by a lamp is generally described by two parameters; the correlated colour temperature and the CIE general colour rendering index. respectively For most applications there is a minimum requirement for the colour rendering properties of the lamps used and the correlated colour temperature of the source is generally chosen for the atmosphere that the lighting is designed to produce.4.7 Run-up timeWhen a lamp is switched on it takes a certain amount of time to reach full light output. The usual measure used to assess run-up time is the time that it takes for a lamp to reach 80% of its full output. For a GLS lamp this might be a fraction of a second, while for low pressure sodium this could be as much as 20 minutes. For some applications such as road lighting the run-up time is not important. However, for occasionally used rooms in a home it is very important.4.8 Restrike timeWhen some gas discharge lamps go out due to an interruption in the mains supply it is not possible to restart them until the lamp has cooled down. This may take several minutes. The use of lamps with a long restrike time may cause problems in some installations due to the possibility of a small power outage causing a long blackout.3.4.9 Other factorsThere are also many other factors that impact upon the use of lamps in a particular application. These factors include the following.Lamp size: some lamps are too large for certain applications, whilst some small lamps may produce too high a luminance for others.Dimming: it is not possible to dim all lamp types and some types may be only dimmed down to given percentage of their output. Dimming for some lamps may require the use of special control gear.Ambient temperature: not all lamps will run at a given temperature. For example some compact fluorescent lamps are not suitable for outdoor use as they will not start if they are too cold.

5. Luminaires5.1 Basic requirementsA luminaire is the apparatus containing the light source. A luminaire is designed to: Connect the light source to the electricity supply Protect the light source from mechanical damage Control the distribution of light Be efficient Withstand the expected conditions of use Be safe when used in the recommended manner. To meet these design objectives it is necessary to consider the electrical, mechanical, optical, thermal and acoustic aspects of luminaires.5.1.1 ElectricalElectrical wiringThe internal wiring of a luminaire has to be capable of handling the electrical current and the thermal conditions in the luminaire. The cross sectional area of the wire will determine the maximum allowable current. IEC 598 specifies a minimum cross section of 0.5 mm2 although this may be reduced to 0.4 mm2 where space is severely restricted. The wire itself can be solid or stranded. Solid wire is easier to hold in position and to strip, making it simpler to install in a luminaire. However, solid wire is not suitable for luminaires that are subject to vibration or for luminaires that may be frequently adjusted. For such luminaires, stranded wire is better. Both types of wire are covered with insulating material. The choice of insulation material is largely determined by its heat resistance. The wiring of a luminaire has to be capable of withstanding not only the air temperatures inside the luminaire but also the surface temperatures of components that the wiring may contact, such as lamps, control gear and lamp holders. PVC insulation that is heat resistant up to 90 C, 105 C and 115 C is available. Where higher temperatures may be experienced, silicon rubber (170 to 200 C) and PTFE (250 C) insulation may be used. Additional thermal insulation can be achieved by covering the electrical insulation with a glass fibre sleeve. Connection to the electricity supply There are three approaches commonly used to connect a luminaire to the electricity supply; the connection block, automatic connection and through wiring. The most common method is via a connection block within the luminaire. To prevent the connection being accidentally broken, the supply wire should pass through a cable clamp before reaching the connection block. Luminaires mounted on trunking systems are often designed so that connection to the electricity supply occurs when the luminaire is mounted on the trunking. For this to occur the electrical socket carrying the electricity supply is part of the trunking and the plug is contained within the luminaire.The earth pin of the plug is longer than the live and neutral pins so that when the luminaire is offered up to the track, the earth connection is made before the live and neutral, and when removing the luminaire, the live and neutral connections are broken before the earth. Through wiring is a system for connecting a series of luminaires in parallel across a supply cable. This reduces the amount of cabling required and speeds up installation. The supply cable should have a cross section of 2.5 mm2 as a minimum, but the wiring from the connection block in each luminaire may have a smaller cross section, typically 0.5 or 0.75 mm2.EarthingMetal parts of Class 1 luminaires (see Section 4.3.2, Table 4.11) that are accessible when the luminaire is installed or open for maintenance or that may become live if the insulation fails should be permanently connected to an earth terminal. The wire used for earthing should be at least 2.5 mm2 in cross section.5.1.2 Mechanical The mechanical integrity of a luminaire depends on the materials used and the quality of its construction. Materials Steel Many interior lighting luminaires are made from ready-painted sheet steel, white being the usual paint colour. Where corrosion is a problem, galvanised sheet steel is used. Where a very durable paint finish is required, enamelling is used. Stainless steel Stainless steel is rarely used for luminaire bodies but it is widely used for many small, unpainted luminaire components that have to remain free from corrosion. Aluminium sheet Aluminium sheet is mainly used for reflectors in luminaires. It can have good reflection properties and the physical strength to form stable reflectors of the desired form. Cast aluminium Cast aluminium is widely used for floodlight housings. Such housings are light in weight and can be used in damp or corrosive atmospheres without any further treatment provided that the correct grade of aluminium has been used. Plastics There are many different forms of plastic used in luminaires, either for complete housings or components. These plastics differ in their transparency, strength, toughness, sensitivity to UV radiation and heat resistance. Glass Three types of glass are used in luminaires; soda lime glass, borosilicate glass, and very high resistance glass. Soda lime glass is used where there are no special heat resistance demands. Where high heat resistance, chemical stability and resistance to heat shock are required, borosilicate glass is used. High resistance glass has the advantage that it can deliver high heat resistance, high thermal shock resistance and great physical strength even in thin sheets. CeramicsSome components of luminaires that produce very high temperatures are made of ceramics.ConstructionAll luminaires should be designed to withstand the rigours of transport to the site, installation and prolonged use. Generally, exterior luminaires need to be more substantial than those designed for interior use. Some luminaires are designed to resist the ingress of foreign objects, dust and moisture. Such luminaires have a transparent front cover and all points of access to the luminaire have a seal. Front covers are usually made of glass or plastic. Where there is a risk of physical impact, as in a sports hall, glass or acrylic front covers need to be covered with a wire screen. If a polycarbonate front cover is used, no such screen is necessary. As for the seals, these come in various forms from a simple felt seal to convoluted notched rubber seals. The effectiveness of these seals is quantified by the IP classification system. 5.1.2 Optical controlOptical control of the light output from a light source is achieved by some combination of reflectors, refractors, diffusers, baffles or filters.ReflectorsThree types of reflector are used in luminaires; specular, spread and diffuse.Specular reflectors are used when a precise light distribution is required. The shape of the reflector and its position relative to the light source determine the light distribution. The most common shapes for reflectors are circular, parabolic and elliptical.A circular reflector with a point light source at its focus will produce a light distribution of the type shown in the below figure, reflections from some parts of the reflector being almost parallel while those from parts of the reflector away from the axis are divergent. This type of circular reflector is used in cylindrical form for picture lighting using tubular incandescent and fluorescent light sources.

The light distribution from a circular reflector with a point light source at its focus.

A circular reflector with a point light source at its centre of curvature produces a light distribution of the type shown in the below figure. This type of reflector is widely used in projection systems and spotlights to increase the amount of light delivered to the associated lens system.

The light distribution from a circular reflector with a point light source at itscentre of curvature

A parabolic reflector with a point light source at its focus produces a parallel beam of reflected light. Moving the light source in front or behind the point of focus will cause the beam to converge or diverge. The parabolic reflector is widely used in spotlight design either exactly, when the reflector is smooth, or approximately, when the reflector is facetted.

The light distribution from a parabolic reflector with a point light source at its focus. The beam intensity will be greater at the centre than at the edge compare cones aFb and AFB.

An elliptical reflector with a point light source at one focus will ensure that the reflected rays all pass through the second focus (Figure 4.4) Elliptical reflectors in trough form are widely used for tubular fluorescent luminaires.

Elliptical reflectors showing the change in light distribution as the point light source is moved relative to the first focus (F).Spread reflectors are deliberately distorted specular reflectors. They can be circular, parabolic or elliptical in cross section and spherical or cylindrical in form. The distortion takes the form of modulating the specular surface of the reflector by hammering (peening) to produce a regular array of dimples, or by etching or brushing the surface. The advantage of this distortion is that it smears out variations in light distribution caused by inaccuracies in the manufacture of the reflector and the size of the light source. Spread reflectors are used where a well-defined but even light distribution is required.Diffuse reflectors are the opposite of specular reflectors. Unlike a specular reflector, the shape of a diffuse reflector has only a small effect on the light distribution. Diffuse reflectors are used where there is a need to redirect light with a very wide beam.Many different materials are used in reflectors. Typical values of reflectance for these materials are given in the below table.

DiffusersDiffusers are transparent materials that scatter light in all directions. They provide no control of light distribution but do serve to reduce the brightness of the luminaire. Diffusers are commonly made of materials that maximise light scatter and minimise absorption, such as opal glass or plastic.BafflesBaffles can have three functions; to hide the light source from common viewing angles, to reduce the amount of spill light, and to control the light distribution.The extent to which the light source is hidden from view is quantified by two angles, the shielding angle and its complementary, the cut-off angle. The shielding angle is the angle between the horizontal and the direction at which the light source ceases to be visible. The below figure shows the shielding angle for a simple fluorescent luminaire.

If the purpose is to hide the light source and also to control light distribution, the louvre is made from a specularly reflecting material and shaped so as to direct light downwards and hence increase the shielding angle. As a general rule, the finer the louvre and hence the more the light source is hidden, the lower will be the light output ratio of the luminaire.

6.Luminaire typesThe lighting industry produces many thousands of different luminaires. Given below are briefoutlines of the main types of luminaire used in interior and exterior lighting.Details of any specific luminaire are best obtained from the manufacturers.6.1 Interior lightingDirect luminairesDirect luminaires are luminaires in which the light distribution is predominantly downward. Such luminaires are typically recessed into or surface mounted on the ceiling.They are widely used in offices where the ceiling height is restricted. The usual light source is a fluorescent lamp, either linear or folded. Many different forms of optical control are available, from diffusers through prismatic refractors to parabolic reflectors and louvres. Consequently, direct luminaires are available with a wide range of luminous intensity distributions. Direct luminaires are available for operation in dirty, corrosive or hazardous conditions. Direct luminaires are available with dimming or switching facilities linked to manual, occupancy sensor and photocell control. The most common problems with lighting installations using direct luminaires is the creation of a dark ceiling and poor illuminance uniformity in obstructed spaces. This problem can be overcome by choosing direct luminaires with a little upward light output or by having high reflection factors in the space. Figure 4.10 shows a direct luminaire.

Indirect luminairesIndirect luminaires are luminaires in which the light distribution is predominantly upward. Such luminaires can be suspended below the ceiling, wall mounted or free standing. They require a clean, white ceiling for efficient operation. Indirect luminaires are most practical where the ceiling height is over 2.75 m. The usual light source in suspended indirect luminaires is a linear fluorescent lamp. Wall mounted and free-standing indirect luminaires tend to use a high intensity discharge lamp. Optical control is confined to ensuring that the light output from the luminaire is widely spread across the ceiling so that no hot spots of high luminance are apparent. While indirect luminaires have a high light output ratio, lighting installations using indirect luminaires are usually less energy efficient than those using direct luminaires because of the losses caused by having to use the ceiling as a secondary reflector. This is compensated by the bright appearance of the space, the high level of illuminance uniformity and the absence of discomfort glare.

Direct/indirect luminairesDirect/indirect luminaires are luminaires in which the light distribution is evenly divided between the upward and downward directions. In many ways, direct/indirect luminaires provide the best of both worlds. The energy efficiency of a lighting installation using direct/ indirect luminaires will be higher than that of one using indirect luminaires but the problems of dark ceilings and poor illuminance uniformity are reduced by the indirect component. Direct /indirect luminaires are suspended below the ceiling. They are difficult to use where the ceiling height is below about 2.75 m. The usual light source in direct/indirect luminaires is a linear fluorescent lamp. Optical control is different for the two directions of light output, being much tighter for the downward component than the upward. Direct/indirect luminaires are available with individual dimming of the direct component.

DownlightsDownlights are a form of direct luminaire characterised by a small light emitting aperture. Downlights are usually recessed into the ceiling so they direct all of their light output downward. They are widely used in shops, hotels and other places where a lighting installation with a discreet appearance is desired. Many different light sources can be used in downlights, the most common being incandescent, tungsten halogen, compact fluorescent and metal halide. Through the use of reflectors, louvres, lenses and refractors many different beam spreads and beam sizes are possible (see Section 4.3.2). Some downlights allow for adjustable aiming which is useful when the intention is accent lighting. A number of downlights are fitted with decorative elements directly beneath the downlight aperture to give an impression of brightness to the luminaire. The most common problems with lighting installations using an array of downlights to create uniform illumination are poor illuminance uniformity caused by overspacing and dark ceilings. Care is necessary to avoid a fire hazard when recessing downlights into an insulated ceiling.

SpotlightsSpotlights are narrow beam luminaires with beam spreads in the range 5 to 30 degrees. They are usually mounted on either a base plate or lighting track. When track mounted, spotlights can be obtained for operation at mains voltage, low voltage or extra low voltage, the latter requiring the installation of a step-down transformer. Spotlights are widely used in shops, hotels and museums for accent lighting. Spotlights are available that use incandescent, tungsten halogen, metal halide and extra high pressure sodium light sources of small physical size. Some incandescent and tungsten halogen light sources can be used as spotlights themselves because they have reflectors giving the desired beam spread built in. Other light sources have to use reflectors to attain optical control. Filters mounted in front of the spotlight can be used to change the light colour. Irises and baffles mounted in front of the spotlight can be used to modify the beam shape. Care is necessary when using spotlights to avoid glare to passers by. Figure 4.14 shows a selection of spotlights.

Task lightsTask lights are a necessary part of a task/ambient lighting system. They provide local lighting of a specific area by bringing the light source closer to the task. The value of task lights is that they enable the user to have some control of the amount and distribution of light on the task by switching or dimming the light source and by changing the position of the luminaire relative to the task. Typically, the light sources used in task lights are incandescent, tungsten halogen or compact fluorescent. The degree of adjustment available can vary widely as can the amount of desk space taken. When selecting task lights attention should be given to the coverage area for common positions and the likelihood of glare to the user. Figure 4.16 shows a selection of task lights.

6.2 Exterior lightingRoad lighting luminaires Road lighting luminaires used for lighting traffic routes are designed to deliver light to a road so that the surface is seen to be of uniform luminance and objects on the road can be seen in silhouette. The light distribution is therefore dependent on the position of the luminaire relative to the road. Most road lighting luminaires are mounted on columns placed at regular intervals at the side of the road or between crash barriers in the median. A few installations use a catenary system in which the luminaires are suspended over the median in a continuous series. For conflict areas and subsidiary roads. The luminaires are designed with a wide light distribution so as to give a uniform illuminance across the road. The light sources used in road lighting luminaires are typically low pressure sodium, high pressure sodium or metal halide. Road lighting luminaires are often provided with adjustable lamp holders and/or reflectors so as to allow the light distribution to be optimised for the light source and road layout. Two broad classes of road lighting luminaire are semi-cutoff and full cutoff. These classes reflecting a different balance between luminaire efficiency and the control of glare. Road lighting luminaires need protection against dust and moisture and so are classified according to the IP system. They are almost always fitted with a photoelectric control package.

Post topsPost top luminaires are a form of road lighting luminaire but unlike the road lighting luminaires described above, which are intended for the lighting of high speed traffic routes, post top luminaires are intended for urban areas, where pedestrians are considered as important as drivers and the decorative aspect of the luminaire is as important as the functional. Post top luminaires are available with either rotationally symmetric or road lighting light distributions, so that the same luminaire can be used to light both roads and open pedestrian areas in a city. Post top luminaires take many different forms, some mimicking traditional styles for historic areas, while others represent the latest design trends. Because of their use in urban areas, low pressure sodium light sources are not used in post top luminaires, the most common light sources being high pressure sodium, metal halide, compact fluorescent and induction lamps. Post top luminaires need protection against dust and moisture and so are classified according to the IP system. Because of their relatively low mounting heights, post top lanterns are often constructed of materials that resist attacks by vandals. They are almost always fitted with a photoelectric control package. The most common problem with post top luminaires is glare. This problem can be avoided if there is no direct view of the light source. Figure 4.18 shows a selection of post top luminaires. Secondary reflectorsSecondary reflector luminaires are designed for use in pedestrianised places such as city squares and parks. In this luminaire, light is directed up from the light source in or on the column and then distributed from a large surface at the top of the column. By changing the area and tilt of the reflecting surface, the light distribution can be altered. Secondary reflector luminaires are inevitably inefficient compared to post top luminaires, but they do not cause glare, are not easily damaged by vandals and can provide a pleasing ambience. Figure 4.19 shows two secondary reflector luminaires.

FloodlightsFloodlights can be used to wash a large surface with light or to pick out a specific feature of a building. Floodlights vary enormously in their size, power and light distribution. The smallest floodlights consist of little more than a 150 W linear tungsten halogen lamp with a spread reflector. The largest consist of a high intensity discharge lamp with power in the kilowatt range and a carefully shaped reflector. The light distribution of a floodlight can be rotationally symmetric, symmetrical about one axis or asymmetrical about one axis. This distribution is usually classified as narrow, medium or wide beam. The light sources used in floodlights include incandescent, tungsten halogen, high pressure sodium and metal halide. Floodlights need protection against dust and moisture and so are classified according to the IP system and are often soundly constructed of materials that resist attacks by vandals. Filters mounted in front of the floodlight can be used to change the light colour. Barn door baffles mounted on the floodlight can be used to modify the beam shape. Care is necessary when using floodlights to avoid glare to passers by. WallpacksAs their name suggests, wall packs are designed to be mounted on walls so as to provide a low level of illumination in the nearby area. They are widely used for security and amenity lighting. The light distribution is usually wide and is achieved by a combination of reflecting and refracting elements. The light sources used in wall packs are usually low wattage low pressure sodium, high pressure sodium and compact fluorescent. Wallpacks need protection against dust and moisture and so are classified according to the IP system (see Section 4.3.2, Table 4.10). Because of their relatively low mounting heights, wallpacks should be solidly constructed of materials that resist attacks by vandals. The most common problem experienced with wallpacks is glare. This problem is much reduced if there is no direct view of the light source. Figure 4.21 shows a selection of wallpacks.

6.3 Operating conditionsThe International Protection (IP) system classifies luminaires according to the degree of protection provided against the ingress of foreign bodies, dust and moisture. The degree of protection is indicated by the letters IP followed by two numbers. The first number indicates the degree of protection against the ingress of foreign bodies and dust. The second indicates the protection against the ingress of moisture.

7. Control gearA wide range of lamps require control gear of some kind to ensure correct running and, in some cases, starting of the lamp. With discharge lamps it is the job of the control gear to limit the current through the lamp whereas with some incandescent lamps the gear is there to reduce the voltage. Some low voltage tungsten lamps need units to supply them with the correct voltage and LEDs need electronics to limit the current going through them. 7.1 Ballasts for discharge light sourcesGeneral principles Control gear for discharge lamps has to perform a number of functions: limit and stabilises lamp current: due to the negative resistance characteristic of gas discharge lamps. It is necessary to control the current in the lamp circuit. ensure that the lamp continues to operate despite the mains voltage falling to zero at the end of each half cycle provide the correct condition for the ignition of the lamp: this generally requires the gear to provide a high voltage and in the case of fluorescent lamps requires a heating current to be passed through the electrodes. As well as these basic functions control gear may also have the following requirements placed on it: Ensure a high power factor Limit the harmonic distortion in the mains current Limit any electromagnetic interference (EMI) produced by the lamp and ballast Limit the short-circuit and run up currents to protect the lamp electrodes and to help the supply wiring system. Keep the lamp current and voltage within the specified limits for the lamp during mains voltage fluctuations.With electromagnetic control gear several separate control components may be needed these may include ballasts, starters, igniters, capacitors and filter-coils.When electronic control gear is used it is common to integrate all the components into one package. The details of the various circuits used are discussed in the following sections.

Electromagnetic control gear for fluorescent light sourcesChoke coils used to be the most common type of current limiting device used with linear and compact fluorescent lamps. The most common circuit is the switch start, see Figure below.

The choke ballast is made from a large number of windings of copper on a laminated iron core. It works on the self-inductance principle and is designed so that impedance of the choke limits the current through the circuit to the correct value for a given lamp and supply voltages. A range of ballasts is available for different lamps and different voltages. Also the ballast design has to be changed if it is to operate at a different mains supply frequency. To start the lamp it is common to use a glow starter. The glow starter switch consists of one or two bi-metallic strips enclosed in a glass tube containing a noble gas. The glow starter is connected across the lamp so it is possible for a current to pass through the ballast, through the electrode at one end of the lamp, through the electrode at the other end of the lamp and back to neutral. When the mains voltage is first applied to the lamp circuit, the total mains voltage appears across the electrodes of the starter and this initiates a glow discharge. This discharge heats the bi-metallic elements within the starter and as the electrodes heat up they bend towards each other until eventually they touch. While the electrodes are touching the current passing through the lamp electrodes pre-heats them. While the electrodes in the starter are touching there is no glow discharge and so the electrodes cool and separate. At the moment that the electrodes come apart the current through the ballast is interrupted causing a voltage peak across the lamp. Note: the glow starter does not always create the conditions for the lamp to start and sometimes the starting cycle has to be repeated a number of times. Figures below illustrate the starting process.

In addition to the ballast and the starter most fluorescent lamps circuits have a capacitor connected across the supply terminals to ensure a high power factor for the circuit. Electromagnetic control gear for HID light sourcesThere are a number of different types of circuits used for high intensity discharge (HID) lamps; they vary according to the type of lamp and its requirements for starting. The most common type of ballast used is a choke or inductive ballast in series with the lamp. The choke, which is a coil of copper wire wound on a laminated iron core, limits the current through the lamp.

This type of circuit is used for all high intensity discharge lamps apart from the low pressure sodium lamp. The low pressure sodium lamp has a long run-up during which time the voltage across the lamp needs to be greater than normal mains voltage; this has given rise to a number of circuits for running the lamp that provide the necessary voltage. The most common of these circuits is the autoleak transformer.

The autoleak transformer works like an autotransformer increasing the supply voltage, but by careful design of the secondary winding it can also act as a choke to control the current through the lamp. Most high pressure sodium lamps and metal halide lamps require a high voltage pulse to start the arc in the lamp. This is usually provided by an electronic ignitor. There are several types of ignitor circuits, the two most common are the semi-parallel and the superimposed pulse type

The semi-parallel ignitor relies on the tapped ballast coil to generate the ignition pulse whereas the superimposed type ignitor has its own coil to generate the pulse. The semi-parallel has many advantages in that it consumes no power when the lamp is running, it is cheaper and lighter but, as it relies on the ballast, it may only be used with the ballast for which it has been specifically designed.Ignitors sometimes have other features built in such as self-stopping ignitors that will not continually try to restrike a lamp that has come to the end of its life. There are also some that are designed to produce extra high voltages that can restrike hot lamps. Electronic control gear for fluorescent light sourcesOperating fluorescent lamps at high frequency has a number of advantages and most modern control gear is now of this type. Most electronic ballasts for fluorescent lamps are integrated into a single package that performs a number of functions. These functions are: A low pass filter: this limits the amount of harmonic distortion caused by the ballast, controls the amount of radio frequency interference, protects the ballast against high voltage mains peaks and limits the inrush current The rectifier: this converts the AC power from the mains supply into DC A buffer capacitor: this stores the charge from each mains cycle thus providing a steady voltage to the circuits that provide the power to the lamps The HF power oscillator takes the steady DC voltage from the buffer capacitor and using semi conductor switches controlled by the ballast controller creates a high frequency square wave The output of the power oscillator is fed through a small HF coil that acts as a stabilization coil to the lamp.

In some ballasts the electronics that control the power oscillator can vary the frequency at which the power oscillator runs; as the frequency increases the current passing through the coils decreases and thus it is possible to dim the lamps. Some types of ballast have a 0 to 10 volt input that is used to regulate the output while some have digital interfaces.Electronic gear for HID light sourcesMaking electronic control gear for HID light sources is a complex process. There are many different lamp types each with different electrical requirements and a limited range of frequencies in which they can be operated. Also many lamp types do not show a significant gain in efficiency when operated on high frequencies. For these reasons electronic control gear has been developed more slowly for HID lamps than for fluorescent lamps. However, it is possible to gain a number of benefits from electronic gear for HID lamps. These include: Increased lamp life Elimination of visible flicker Better system efficacy Less sensitivity to mains voltage or temperature fluctuations The possibility of dimming with some lamp types. Not all these benefits are possible for all lamp types and all control gear combinations. However, the availability and quality of electronic gear available for HID lamps is rapidly increasing. 5.1.2 Transformers for low voltage light sourcesMany tungsten halogen lamps are designed to run on low voltages the most common of which is 12 volts. Thus they need a device to reduce the supply voltage. The traditional way to do this was by using a transformer. Figure below shows the various currents and voltages in a transformer and gives the approximate relationship between the voltages, currents and the number of turns in the primary and secondary coils.

As well as reducing the voltage the transformer also isolates the lamp supply from the mains. This means that even under a fault condition the voltage in the secondary circuit will not rise significantly above the nominal output voltage and so it will always be safe to touch the conductors on the low voltage side. Most modern transformers for halogen lamps involve electronics. They usually contain high frequency oscillators to permit the use of smaller transformers that have smaller power losses. With the introduction of electronics it is possible to introduce additional features such as constant voltage output and soft starting of the lamps. Drivers for LEDsLEDs need to be run at a controlled current to ensure proper operation. To provide this drivers are used. Most drivers take mains power and provide a constant current output. However, it is possible to control some drivers so that output current is varied so that the LED may be dimmed. In more complex systems it is possible to dim three separate channels separately, so that when red, green and blue LEDs are used together it is possible to make colour changes. Most LED drivers can maintain their constant current output over a range of voltages so it is often possible to connect a number of LEDs in series on one driver. 7.2 Lighting controls7.2.1 Options for controlThere are a number of factors that need to be considered in any control system; these are the inputs to system, how the system controls the lighting equipment and what is the control process that decides how a particular set of inputs will impact on the lighting. Thus for a control system to work it must have: input devices: such as switches, presence detectors, timers and photocells control processes: these may consist of a simple wiring network through to a computer based control system controlled luminaires: the system may control luminaires in a number of ways, from simply switching them on and off to dimming the lamp and in more complex systems causing movement and colour changes.

7.2 Input devicesManual inputsThese vary from simple switches used to turn the lights on though dimmer switches and remote control units that interface to a control system to lighting control desks that are used in theatres. The point of these units is to allow people to control the lighting and care is always needed in the application of such devices to ensure that users of the system can readily understand the function of any such control. Presence detectorsMost presence detectors are based on passive infrared (PIR) detectors, however some devices are based on microwave or ultrasonic technology. PIR devices monitor changes in the amount of infrared radiation that they are receiving. The movement of people in a space will be detected by them and this can be signalled to a control system. Thus, if a device detects the presence of a person this can be used to signal the control system to switch the lights on, but if the device has not detected anybody for some time this can be used to signal that there is nobody there and that the lights can be turned off. TimersMost computerised control systems have timers built in so that they can turn the lighting on or off at particular times. However, there are also a large number of time switches available that can turn lamps on an off at given times. There are also timers used in street lighting that change the time that they switch at throughout the year so that the lamps are switched at dawn and dusk. PhotocellsThere are many different types of photocell used to control lighting. The simplest to use are those which switch on at one illuminance value and switch off at another; these are commonly used to turn exterior lights on at dusk and off at dawn. Some photocells communicate the illuminance value to the central control system, which uses the information to adjust the lighting in some way. Some photocells are mounted on ceilings with shields around them so that they only receive light reflected from the working plane, this makes them act like luminance meters and provided the reflectance of the working plane remains constant they can be set up to follow the illuminance of that plane.

8. Lighting curves8.1 Polar Intensity CurvesThis illustrates the distribution of luminous intensity, in cd/1000 lm, for the transverse (solid line) and axial (dashed line) planes of the luminaire. The curve provides a visual guide to the type of distribution expected from the luminaire e.g. wide, narrow, direct, indirect etc, in addition to intensity.

8.2 Cartesian DiagramsGenerally used for floodlights, this indicates the distribution of luminous intensity, in cd/1000 lm, for the horizontal (solid line) and vertical (dashed line) planes of the luminaire. The diagram provides a visual guide to the type of distribution expected from the luminaire e.g. narrow or wide beam etc, in addition to intensity. The associated data illustrates the beam angle to 10% peak intensity.

8.3 Illuminance Cone DiagramsUsually used for spotlights or lamps with reflectors, the diagram indicates the maximum illuminance, Elux, at different distances, plus the beam angle of the lamp over which the luminous intensity drops to 50%. The beam diameter at 50% peak intensity, relative to distance away, is also shown.

8.4 Isolux DiagramsThe contours provide the points of equal illuminance, in lux, on the floor or wall plane, from a specific stated mounting position. The diagram can be used to assess the distribution characteristics of the luminaire in addition to determining lighting levels.

9. Lighting Calculations:

The lighting calculation for a given area involves a clear understanding of not only the various types of luminaires available but also the different factors that affect the distribution of light from these luminaires. Some of the factors that affect the light output of a luminaire are:1. Luminaire design.2. Light source.3. Reflector, design and material.4. Position of lamp source within luminaire.5. Reflector design and material.6. Diffuser design and material.7. Quality and thickness of glass.8. Presence of any wireguards.9. Environmental conditions.10. Frequency and quality of maintenance.An understanding of the above helps in working out the efficiency of the luminaire or the light loss factor which is vital for correct lighting design. While factors 1 to 8 depend upon the luminaire manufacturer. Factors 9 & 10 are dependant upon the user. The quality of maintenance and the amount of dust accumulated on a luminaire can drastically affect the light output. The factors to be taken into account for lighting design are:1. Luminaire light distribution data.2. Luminaire description.3. Sheilding angle of reflectors.4. Coefft, of utilization.5. Reflectance of walls, ceiling, floor.6. Luminaire spacing.7. Luminaire mounting height.8. Beam spread.9. Ambient environment.10. Maintenance factors.

9.1 Lighting calculation using Lumen method:This method it depends mainly on finding and calculating the utilization factor.By definition:E = Fr / A , ---------- (1)E: Illuminance at working area (lux)Fr: Luminous flux in lumensA: area (m2)Taking into consideration that part of the Luminous Flux will reach the working plane then,UF = Fr/FL , ---------- (2)UF: Utilization factorFr: Luminous flux in lumens at working plane.FL: Total Luminous flux in lumens from the luminaire.As a result, Fr = UF x FL ---------- (3)Substituting equation 3 in 1,E = ( FL x UF) / A , ---------- (4)Utilization factor is affected by the following:1. Room surfaces reflectance factors (Ceiling, walls and floor).2. Room dimension.3. Luminaire charectristics.If the lighting unit have more than one lamp thenE = ( n x FL x UF) / A , ---------- (5)n: Total number of lamps in the lighting unitAlso, the lighting output from each lighting unit will be reduced with time due to maintenance issues such as dirt, dust, lamps malfunctioning, lower lumen output with time,etcAll the above will be considered as one factor (maintenance factor MF). Moreover, and taking into consideration the total number of luminaires, the final equation will be :E = ( N x n x FL x UF x MF) / A , ---------- (6) , E: Illuminance at working area (lux).N: Total number of luminaires.n: Total number of lamps in the lighting unitUF: Utilization factorMF: Maintenance factorFL: Total Luminous flux in lumens from the luminaire.A: area (m2)In order to calculate the utilization factor, the room index shall be calculated according to the following formula:Kr = (L x W) / (Hm x (L+W)) , ---------- (7) ,Where:Kr : Room index.L : Room length.W : Room width.Hm : Suspension height for lighting unit. The height is measured from the lighting unit horizontal plan vertically to the working plane.In order to start room lighting design and calculation, the required lux level has to be known. The following tables illustrating required lux level at differen areas:

The following Table illustrates the recommended values for maintenance factor with reference to the surrounding conditions and area usage:Area ConditionMaintenance Factor (MF)Planning Factor (P = 1/MF)

Clean0.81.25

Unclean0.71.43

Dirty0.61.67

After determining the room index value (Kr), the following table could be used to determine the utilization factor (UF). Luminaires TypeCeil-ing70%50%30%

Walls50%30%10%50%30%10%30%10%

RoomIndexUtilization Factors

Direct 0 / 79Maintenance Factor

0.60.81.01.251.52.02.53.04.05.00.370.450.490.530.560.610.660.670.710.720.310.410.450.490.530.580.630.650.680.700.270.370.420.460.490.530.600.620.660.670.360.450.490.530.550.600.640.660.690.710.310.400.450.490.520.570.620.640.670.680.270.370.420.460.490.550.600.620.650.670.310.400.450.480.510.560.610.630.660.670.270.370.420.460.490.550.600.610.640.66

Semi-direct 25 / 60Maintenance Factor

0.60.81.01.251.52.02.53.04.05.00.270.350.370.430.460.500.550.580.620.640.250.290.340.380.410.460.500.530.570.600.190.260.300.340.370.420.460.490.530.560.260.330.360.400.430.470.510.530.570.590.220.280.320.360.390.430.470.490.530.550.160.250.290.320.350.400.440.460.510.520.200.270.300.330.370.400.440.460.500.510.180.240.280.310.330.380.420.440.480.49

General Direct 39 / 45Maintenance Factor0.60.81.01.251.52.02.53.04.05.00.240.290.330.370.400.450.480.510.550.570.190.250.280.320.360.400.430.460.500.530.160.220.260.290.310.360.390.420.470.490.220.270.300.330.360.400.430.450.490.510.180.230.260.290.320.360.390.410.450.470.150.200.240.260.290.330.360.380.420.440.160.210.240.260.290.320.340.370.400.410.140.190.210.240.260.290.330.340.380.40

Semi-indirect 66 / 20Maintenance Factor

0.60.81.01.251.52.02.53.04.05.00.200.240.280.310.340.380.420.450.490.510.160.200.240.270.300.340.380.410.450.470.130.180.210.240.270.310.350.370.420.440.160.200.230.260.280.310.340.360.390.410.130.170.190.220.240.270.300.320.360.380.110.150.170.200.220.250.280.300.340.360.100.130.150.170.190.210.230.250.270.280.090.120.130.150.170.190.220.230.250.27

Indirect 80 / 0Maintenance Factor0.60.81.01.251.52.02.53.04.05.00.150.190.220.260.280.320.350.380.420.430.110.150.190.220.240.280.310.340.390.410.100.130.160.190.210.250.290.310.360.380.090.120.140.170.190.210.230.250.270.290.080.100.120.140.160.180.210.220.250.270.060.090.100.130.140.170.190.210.240.250.040.060.070.080.090.110.120.130.150.160.030.040.050.070.080.100.110.120.140.15

Engineers Training Center02 - Page 73 of 73Electrical "Building Installation" Lighting