LIGHT CONTROLLIGHT CONTROLLIGHT CONTROLLIGHT CONTROL

TYPES OF LIGHTING SCHEMETYPES OF LIGHTING SCHEMETYPES OF LIGHTING SCHEMETYPES OF LIGHTING SCHEME

• The distribution of light emitted by lamps is usually controlled to some extent by means of reflectors and translucent diffusing screens, or even lenses.

• The interior lighting schemes may be classified as

Direct lighting :-

• It is most commonly used type of lightening schemes.

• In this more than 90% of total light flux is made to fall directly on working planes with the help of deep reflectors.

• It causes hard shadows and glare• It causes hard shadows and glare

• Mainly used for industrial and outdoor lightning.

Semi-direct lighting :-

• In this 60 to 90% of total light flux is made to fall downwards directly on working planes with the help of semi direct reflectors, remaining light is used to illuminate the ceiling and walls.

• It is best suited for rooms with high ceilings where high level of uniformly distributed illumination is desirable.

• Glare in such units is avoided by employing diffusing globes, beyond this it also improve efficiency of system with reference to working plane.

Semi-indirect lighting :-

• In this 60 to 90% of total light flux is thrown upwards to the ceiling for diffuse reflection and the rest reaches the working plane directly except for some absorption by the bowl.

• The lightening scheme is with soft shadows and glare free.

• It is mainly used for indoor light decoration purposes.

Indirect lighting :-

• In this more than 90% of total light flux is thrown upwards to the ceiling for diffuse reflection by using inverted or bowl reflectors.

• In such a system the ceiling acts as the light source, and the glare is reduced to minimum.

• In such a system the ceiling acts as the light source, and the glare is reduced to minimum.

• The resulting illumination is softer and more diffused and appearance of room is much improved over that which results from direct lighting.

• It is used for decoration purposes in cinemas, theatres and hotels etc. and in workshops where large machines and other obstructions would cause troublesome shadows if direct lighting is employed.

General lighting :-

• In this scheme lamps made of diffusing glass are used which give nearly equal illumination in all directions.

DESIGN OF LIGHTING SCHEMESDESIGN OF LIGHTING SCHEMESDESIGN OF LIGHTING SCHEMESDESIGN OF LIGHTING SCHEMESThe lighting scheme should be such that it may,

1. Provide adequate illumination,

2. Provide light distribution all over the working plane as uniform as possible,

3. Provide light of suitable colour, and

4. Avoid glare and hard shadows as far as possible.

The following factors are required to be considered while designing the lighting scheme,

a. Illumination level :-

• This is the most vital factor because a sufficient illumination is the basic means whereby we are able to see our surroundings.

• For each type of work there is a range of brightness most favourable to output i.e. which causes minimum fatigue and gives maximum output in terms of quality depends upon:

(i) The size of the objects to be seen and its distance from the observer. Greater the distance of the object from observer and smaller the size of the object, greater will be the illumination required for its proper perception and

(ii) Contrast between the object and back-ground-greater the contrastbetween the colour of the object and its background, greater will be theillumination required to distinguish the object properly. Objects which areseen for longer duration of time required more illumination than those forcasual work. Similarly moving objects required more illumination than thosefor stationary objects.

t-1 Illumination level required, as per ISI, in various parts of a buildingt-2 Illumination level required, as per ISI, for various types of traffic routes.

b. Uniformity of Illumination :-

• The human eye adjusts itself automatically to the brightness within the field of vision.

• If there is a lack of uniformity, pupil or iris of the eye has to adjust more frequently and thus fatigue is caused to the eye and productivity is reduced.

• It has been found that visual performance is best if the range of brightness within the field of vision is not greater than 3:1, which can be achieved by employing general lighting.

c. Color of Light :-

• To measure the color, CCT (Correlated Color Temperature) and CRI (Color Rendering Index) are calculated to provide a suitable color appearance in the lighting design Index) are calculated to provide a suitable color appearance in the lighting design scheme.

• CCT or Correlated Color Temperature means the temperature of the black body at which this black body radiation color is equivalent to the color of the lamp lumens.

• CRI or Color Rendering Index means degree of closeness of the color of lumens from the lamps to the standard Lumen color.

• There are five types of “white” fluorescent lamps available in the market.

• The first three types i.e. warm white, cool white and day light lamps and they are with high efficacy to provide reasonable color rendition.

• Next two types are the two deluxe lamps which have only 70% of the efficacy but they provide improved color rendition.

• The words warm, cool and daylight are chosen in the sense that a warm white lamp emits yellowish white light and makes a space feel warmer.

• Whereas, a cool white lamp emits a bluish white light and it tends to create a cooler atmosphere.

d. Shadows :-

• In lighting installations, formation of long and hard shadows causes fatigue of eyes and therefore is considered to be a shortcoming.

• Complete absence of shadows altogether again does not necessarily mean an ideal condition of lighting instillations.

• Contrary, perhaps to popular opinion, a certain amount of shadow is desirable in artificial lighting as it helps to give shape to the solid objects and makes them easily artificial lighting as it helps to give shape to the solid objects and makes them easily recognized.

e. Glare :-

• It may be direct or reflected i.e. it may come direct from the light source or it may be reflected brightness such as from a desk top, nickeled machine parts, or calendared paper.

• Direct glare from a source of light is more common, and is more often a hindrance to vision.

• A glance at the sun proves that an extremely bright light source causes acute eye discomfort.

• Reflected glare is glare which comes to the eyes as glint or reflection of the light source in some polished surface.

f. Mounting Height :-

• In case of direct lighting it depends upon the type of building and type of lighting scheme employed.

• For rooms of large floor area, the luminaries should be mounted close to ceiling as possible.

• In case of indirect and semi-indirect lighting, it would be desirable to suspend luminaries enough down from ceiling to give uniform illumination.

g. Colour of surrounding Walls :-

• The illumination in any room depends upon the light reflected from the walls and ceilings.and ceilings.

• White walls and ceilings reflect more light as compared to coloured ones.

h. Spacing of Luminaries :-

• The distance of light source from the wall should be equal to one half the distances between two adjacent light sources.

• The distance between light fittings should not exceed 1.5 times the mounting height.

• In the case of direct and semi-direct luminaries the ratio of the horizontal spacing between rows to the height of the lumi-naries above the working plane depends to quite an extent on the candle power-distribution curve of the luminaire.

• With fluo-rescent luminaries it is good practice to aim at a value of unity forthis ratio, and to set an upper limit of 3/4.

• In the case of tungsten lamps combined with focusing reflectors, the ratio ofspacing to height should be about 0.6.

• In the case of indirect and semi-indirect luminaries, it is good practice to aimat a horizontal spacing between rows approximately equal to a height of theceiling above the working plane, and in no case should the horizontal spacingexceed 1½ times this height.

• In the case of fluorescent luminaries, it is a common practice to join two ormore luminaries end to end so that they can share a common outlet.

• In fact it often works out well to use continuous rows of luminaries, especiallywhen the specified illumination is fairly high.

Methodology of Lighting System Energy Methodology of Lighting System Energy Methodology of Lighting System Energy Methodology of Lighting System Energy

Efficiency StudyEfficiency StudyEfficiency StudyEfficiency Study

• A step-by-step approach for assessing energy efficiency of lighting system is given below:

• Step–1: Inventorise the Lighting System elements, & transformers in the facility as per following typical format (Table – 8.2 and 8.3).

• In case of distribution boards (instead of transformers) beingavailable, fuse ratings may be inventorised along the abovepattern in place of transformer kVA.

• Step–2: With the aid of a lux meter, measure and document thelux levels at various plant locations at working level, as daytimelux and night time lux values alongside the number of lamps "ON"during measurement.

• Step–3: With the aid of portable load analyzer, measure anddocument the voltage, current, power factor and powerconsumption at various input points, namely the distributionboards or the lighting voltage transformers at the same as that ofthe lighting level audit.

• Step–4: Compare the measured lux values with standard values asreference and identify locations as under lit and over lit areas.

• Step–5: Collect and Analyse the failure rates of lamps, ballasts andthe actual life expectancy levels from the past data.the actual life expectancy levels from the past data.

• Step–6: Based on careful assessment and evaluation, bring outimprovement options, which could include :

• i) Maximise sunlight use through use of transparent roof sheets,north light roof, etc.

• ii) Examine scope for replacements of lamps by more energyefficient lamps, with due consideration to luminiare, colorrendering index, lux level as well as expected life comparison.

iii) Replace conventional magnetic ballasts by more energy efficient ballasts, with due consideration to life and power factor apart from watt loss.

iv) Select interior colours for light reflection.

v) Modify layout for optimum lighting.

vi) Providing individual / group controls for lighting for energy efficiency such as:

a. On / off type voltage regulation type (for illuminance control)

b. Group control switches / units

c. Occupancy sensors

d. Photocell controls

e. Timer operated controls

f. Pager operated controls

g. Computerized lighting control programs

vii) Install input voltage regulators / controllers for energyefficiency as well as longer life expectancy for lamps wherehigher voltages, fluctuations are expected.

viii) Replace energy efficient displays like LED's in place of lamptype displays in control panels / instrumentation areas, etc.

Factory LightingFactory LightingFactory LightingFactory LightingFactory LightingFactory LightingFactory LightingFactory Lighting

Adequate lighting of factories is of vital importance, as it provides improved amenities for the employees, increased production and has a definite economic value in reducing accidents with their consequent loss of time and compensation payments.

General Requirements and Types of Installations for Factory Lighting :-

• A factory lighting installation, in common with other indoor equipment's should provide an adequate illumination on the working plane and give a good distribution of light, employ simple and easily cleaned fittings and avoid glare.

• It is essential not only to avoid glare from the lamp itself but also reflected glare from any polished surface, which may be within the line of vision.glare from any polished surface, which may be within the line of vision.

i. General Lighting :-

• The usual scheme in factories and workshops is to mount a number of lamps at a sufficient height.

• Due to this uniform distribution of light over the working plane is obtained.

• In large machine shops the height is governed by the necessity of keeping the lamps above the travelling crane.

• Since light colored walls and ceiling add to the effectiveness of an installation, therefore; it is necessary to get whitewashing or painting done.

ii. Local Lighting :-

• For fairly intense illumination, local lighting can be provided by means of adjustable fittings attached to the machine.

• Such lamps should be mounted in deep reflectors so that glare is avoided.

• Portable hand lamps(Upto 50V) attached to wall plugs by means of trailing leads are used for maintenance work and emergency lighting and also danger of shock is also avoided in these few volt lamps.

• The supply for such lamps can be obtained from a special low voltage distribution system running throughout the factory or by means of a small transformer for each individual lamp.small transformer for each individual lamp.

iii. Emergency Lighting :-

Some lights, such as for:

(i) Internal pilot lighting required for safe and speedy evacuation of personnel after main lighting circuit is off.

(ii) External pilot lighting, provided with careful shades leading to shelters required for evacuation of personnel.

(iii) For control posts, first aid centers etc.

(iv) Dials and gauges in important plants required to be watched regularly are required during an air raid when all the factory lights are off as a matter of air-raid precaution.

• The circuit supplying the above emergency lights should be independently controlled.

• It is very desirable to provide auxiliary lighting from the source other than the main electric supply preferably from batteries or from small petrol driven generator set.

• If, however, emergency lighting circuits are operated from • If, however, emergency lighting circuits are operated from main electric supply, these should be completely separated from main lighting circuit.

INDUSTRIAL LIGHTING FITTINGSINDUSTRIAL LIGHTING FITTINGSINDUSTRIAL LIGHTING FITTINGSINDUSTRIAL LIGHTING FITTINGSINDUSTRIAL LIGHTING FITTINGSINDUSTRIAL LIGHTING FITTINGSINDUSTRIAL LIGHTING FITTINGSINDUSTRIAL LIGHTING FITTINGS

1. Standard Reflectors :-

• These reflectors are made to accommodate lamps of ratings from 40 to 1500W.

• They give adequate and uniform illumination when they are mounted at a spacing equal to about 1.5 times their mounting height above the working plane.

2. Diffusing Fittings :-

• When more diffused light is required than that given by the standard reflector a diffusing glass screen may be fixed across a standard type of reflector.

3. Concentrating Reflectors:-

• A reflector with a concentrated beam is employed in large machine shops and boundaries, where mounted at a considerable height above the working plane. boundaries, where mounted at a considerable height above the working plane.

• In such a places an ordinary reflector would have too angle of divergence and would waste a great deal of light on walls.

4. Enclosed Diffusing Fittings :-

• An opal globe completely enclosing the lamp giving a very even and well diffused light is used when light coloured walls and ceilings are there.

5. Angle Reflectors :-

• It is used to provide illumination in a vertical plane where concentrating type reflectors are used.

• These can be mounted on suitable stanchions or the walls.

Methods Employed for Methods Employed for Methods Employed for Methods Employed for

Lighting CalculationsLighting CalculationsLighting CalculationsLighting CalculationsLighting CalculationsLighting CalculationsLighting CalculationsLighting Calculations

1. Watts per Square Metre Method :-

• This is principally a “rule of thumb” method, very handy for rough calculation or checking.

• It consists in making an allowance of watts per square meter of area to be illuminated according to the illumination desired on the assumption of an average figure of overall efficiency of the system.

2. Lumen or Light Flux Method :-

• This method is applicable to those cases where the sources of light are such as to produce an approximate uniform illumination over the working plane or where an average value is required.

• From the size of lamp or lamps employed and from their efficiency total lumens • From the size of lamp or lamps employed and from their efficiency total lumens output are determined.

• Multiplying the total lumens output from the source by coefficient of utilization, the lumens received on the working plane are determined.

• If the lamps and surroundings are not perfectly clean, then in determination of lumens received on working plane, the depreciation factor or maintenance factor should be included, i.e.,

Coefficient of Utilization or Utilization Factor :-

• The ratio of lumens reaching the working plane to the total lumens given out by the lamp or lamps, is known as utilization factor or coefficient of utilization

• The value of utilization factor depends upon:

(i) The mounting height of lamps—utilization factor decreases with the increase in mounting height of lamps

(ii) Area to be illuminated—for given height, proportion of direct light becomes more and more if floor area increases, i.e., utilization factor increases with the increase in area to be illuminated

(iii) Type of lighting—more for direct lighting and low for indirect lighting and

(iv) Colors of surroundings etc.— more for light colours and less for dark colours. Its value varies from 0.25 to 0.5 and from 0.1 to 0.25 for direct and indirect lighting (iv) Colors of surroundings etc.— more for light colours and less for dark colours. Its value varies from 0.25 to 0.5 and from 0.1 to 0.25 for direct and indirect lighting schemes respectively.

Maintenance Factor :-

• The illumination loss produced by a lighting installation is considerably less after a year or two of use, it is due partly to the aging of the lamps and partly to the accumulation of dust on the lamps, on the reflecting and transmitting surfaces of the fixtures and on the ceiling and walls.

• This fact is taken into account by including the maintenance factor, which is defined as the ratio of the ultimate maintained meter-candles on the working plane to the initial metre- candles.

• Its value is more if the lamp fittings are cleaned regularly, say 0.8, and less if there is much dust etc. say 0.6.

Depreciation Factor :-

• This is merely the inverse of the maintenance factor and is defined as the ratio of the initial meter- candles to the ultimate maintained meter-candles on the working plane. Its value is more than unity.

• 3. Point to Point or Inverse-Square Law Method :-

• This method is applicable where the illumination at a point due to one or more sources of light is required, the candle powers of the sources in the particular direction under consideration being known.

• If a polar curve of lamp and its reflector giving candle powers of the • If a polar curve of lamp and its reflector giving candle powers of the lamp in different directions is known, the illumination at any point within the range of the lamp can be calculated from the inverse square law.

• If two and more than two lamps are illuminating the same working plane, the illumination due to each can be calculated and added.

• This method is not much used because of its complicated and cumbersome applications.

• It is employed only in some special problems, such as flood lighting, yard lighting etc.

STREET LIGHTINGSTREET LIGHTINGSTREET LIGHTINGSTREET LIGHTINGSTREET LIGHTINGSTREET LIGHTINGSTREET LIGHTINGSTREET LIGHTING

The main objective of street lighting are:

(i) To make the traffic and obstructions on the road clearly visible in order to promote safety and convenience.

(ii) To make the street more attractive.

(iii) To increase the community value of the street.

• The principle employed for street lighting is different from that of interior lighting.

• Because of areas to be illuminated being large, the value of illumination for economic reasons, is very low compared to that for indoor lighting and the question of color rendering is also of minor importance.and the question of color rendering is also of minor importance.

• High level of illumination is not necessary, because firstly one has seldom to look continuously at nearby objects, secondly it is the impression of whole scene that is required.

• In fact in case of interior lighting the objects are seen by the light reflected by them but in case of street lighting the objects are seen in relatively bright back ground i.e., silhouetted against a relatively bright back ground.

• Furthermore, owing to the low illumination, the eye is in its most sensitive state and, therefore, glare must be avoided.

Two general principles are usually employed in the design of street lighting

installations, namely:

(i) The diffusion principle and

(ii) The specular reflection principle.

1. Diffusion Principle :-

• In this case the lamps fitted with suitable reflectors are used.

• The reflectors are so designed that they may direct the light downwards and spread as uniformly as possible over the road surface.

• In order to avoid glare the reflectors are made to have a cut-off of between 30°to 45° so that the filament is not visible except from underneath it.

• The diffusing nature of the road surface causes the reflection of a certain proportion of the incident light in the direction of the observer, and therefore, the road surface appears bright to the observer.

• The illumination at any point on the road surface is calculated by applying point to point or inverse-square law method.

• Over certain proportions of the road the surface is illuminated from two lamps and the resultant illumination is the sum of the illuminations due to each lamp.

2. Specular Reflection Principle :-

• In this case the reflectors are curved upwards so that the light is thrown on the road at a very large angle of incidence.

• It is observed that a motorist requires to see objects about 30 meters away as shown in fig.

• Much of the light from the lamp L3 is not reflected towards the observer, whereas most of the light from lamps L1 and L2 is reflected towards him. Thus the object will appear silhouetted against the bright road surface due to lamps at a longer distance.

• The requirement of a pedestrian, who requires to see objects in his immediate neighborhood, is also fulfilled in this method as some light from the lamps falls

• The requirement of a pedestrian, who requires to see objects in his immediate neighborhood, is also fulfilled in this method as some light from the lamps falls directly downwards.

• This method of street lighting is only suitable for straight sections of the road.

• This method is more economical also as compared to the diffusion method of lighting but it suffers from the disadvantage that it produces glare for the motorists.

Illumination Level for Street Lighting and Mounting Height of Lamps:

• The illumination required depends upon the class of street lighting installations.

• In class A installations, i.e., in important shopping centers and road junctions, illumination level of 30 lumens/m is required where as a in poorly lighted suburban streets, illumination level of 4 lumen/m2 is sufficient.

• An average well-lighted street, will require illumination level between 8 to 15 lumens per square meter.

• Excellent illumination is considered when the distance apart is not more than 8 times the height of the luminaires; that is, with the luminaires 8 meters above street level, they should be spaced not more than 64 meters.meters above street level, they should be spaced not more than 64 meters.

Types of Lamps for Street Lighting :-

• Mercury vapor and sodium discharge lamps have been found to have certain particular advantages for street lighting purposes; the most important of these is the lower power consumption for a given amount of light, which, inspite of the higher cost of the lamps makes the overall cost of an installation with discharge lamps less than that employing filament lamps.

• The color and monochromatic nature of the light produced by discharge lamps do not matter much in street lighting installations.

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11/03/2013