,BSS (Questions)Daylight factorIn architecture, a daylight factor is the ratio of the light level inside a structure to the light level outside the structure. It is defined as:DF = (Ei / Eo) x 100%where, Ei = illuminance due to daylight at a point on the indoors working plane, Eo = simultaneous outdoor illuminance on a horizontal plane from an unobstructed hemisphere of overcast sky.It is impracticable to express interior daylighting in terms of illumination actually obtainable inside a building at any time. For practical purposes Daylight Factor (DF) is used. Its the percentage ratio of the instantaneous illumination level at a reference point inside a room to that occurring simultaneously outside in an unobstructed position.Daylight factor is measured as the ratio of illumination at the working plane inside a room to the total light available outside. This is called daylight factor which is expressed in %.DF includes the following :Sky component (SC): direct light from a patch of sky visible at the point consideredExternal Reflected Component (ERC): light reflected from an exterior surface and then reaching the point consideredInternal Reflected Component (IRC): light entering through the window but reaching the point only after reflection from an internal surface.Glare & Types of GlareThe term 'glare' refers to a certain course (state) of vision at which there appears a sensation of discomfort or the capacity of recognizing objects is reduced or when both these effects are present due to an incorrect distribution of luminance, inappropriate range of luminance or excessive spatial and time-related contrasts.As regards its effects, there are the following types of glare:disturbing - reduces vision capability for a very short but perceptible time, without causing discomfort. The excessive amount of light that reaches the eye is dispersed in the optical centres of the eye, which causes superimposition of the so-called veiling luminance on a correctly focused image of the observed object. An example of this type of glare is when after observing the bulb glower for a short time we try to thread a needle. The fact of perceiving "scotomata" (veiling luminance superimposed on the observed image) for a short but perceptible time makes it impossible to perform this action;annoying - causes unpleasantness, discomfort or irritation and lack of concentration without reducing vision capability. Immediately after removing the cause of glare the discomfort ceases. This glare depends on: the luminance of the particular sources of glare, luminance of the background of the sources, the angular diameters of those sources, their positions in relation to the observer and the number of sources in sight. An example of this type of glare is when we observe an open space evenly covered with clean snow on a sunny day. In every direction we look the white snow seems to dazzle the eyes and causes discomfort;blinding - strong enough to make any object impossible to be seen for a perceptible period of time. This is an extreme case of interfering glare. An example of this type of glare is when in an unlit road at night, from the opposite direction there suddenly appears a car with its headlights on. As a result of the glare, we lose vision for a short but perceptible time.LEDLED lights are widely used as replacement of bulbs in general lighting.Extremely energy efficient and extremely long-lasting light bulbs. An LED light bulb can reduce energy consumption by 80-90% and last around 100,000 hours.They even light up faster than regular bulbs. They are more expensive presently.Widely used in hotels, hospitals, restaurants, jewellery showrooms, exhibitions, art galleries, cosmetic counters, museums, factories, gymnasiums, yards, advertising boards, streets, buildings, lawns and gardens, house holds and places where spot lighting is needed and other general lighting.LED lights save energy and is green which is why it is important to convert to LED - also helps us to control the global warming up to some extent.Advantages:Energy consumption 1/10 of incandescent.High levels of brightness and intensity.Low voltage and current requirement.Low radiated heat - Low operating temperature - (vs. halogen which can be over 600F).High reliability (resistant to shock and vibrations).Instant cold start.Reduced maintenance.Contains no mercury (fluorescent has 10 - 40mg Hg per bulb).Compatible with dimmer switches can be easily controlled and programmed.Long source life.Contain no toxic elements, and last so long that disposal is not much of an issue.Color Rendering IndexColor rendering describes how a light source makes the color of an object appear to human eyes and how well subtle variations in color shades are revealed. The Color Rendering Index (CRI) is a scale from 0 to 100 percent indicating how accurate a "given" light source is at rendering color when compared to a "reference" light source.The higher the CRI, the better the color rendering ability. Light sources with a CRI of 85 to 90 are considered good at color rendering. Light sources with a CRI of 90 or higher are excellent at color rendering and should be used for tasks requiring the most accurate color discrimination.It is important to note that CRI is independent of color temperature (see discussion of color temperature). Examples: A 2700K ("warm") color temperature incandescent light source has a CRI of 100. One 5000K ("daylight") color temperature fluorescent light source has a CRI of 75 and another with the same color temperature has a CRI of 90.The visible part of the electromagnetic spectrum is composed of radiation with wavelengths from approximately 400 to 750 nanometers. The blue part of the visible spectrum is the shorter wavelength and the red part is the longer wavelength with all color gradations in between.Visible SpectrumSpectral power distribution graphs show the relative power of wavelengths across the visible spectrum for a given light source. These graphs also reveal the ability of a light source to render all, or, selected colors.Correlated Color Temprature The correlated color temperature (CCT) is a specification of the color appearance of the light emitted by a lamp, relating its color to the color of light from a reference source when heated to a particular temperature, measured in degrees Kelvin (K). The CCT rating for a lamp is a general "warmth" or "coolness" measure of its appearance. However, opposite to the temperature scale, lamps with a CCT rating below 3200 K are usually considered "warm" sources, while those with a CCT above 4000 K are usually considered "cool" in appearance.The correlated color temperature (CCT) designation for a light source gives a good indication of the lamp's general appearance, but does not give information on its specific spectral power distribution. Therefore, two lamps may appear to be the same color, but their effects on object colors can be quite different. Examples of the CCT of some common light sources are:Tungsten Halogen3000 K"Cool White" Linear Fluorescent4200 KHigh Pressure Sodium1900 K"Warm" Compact Fluorescent2700 KLuminaire A luminaire is defined in Article 100 as, a complete lighting unit consisting of a lamp or lamps together with the parts designed to distribute the light, to position and protect the lamps and ballast (where applicable), and to connect the lamps to the power supply.Efficency of a LuminaireLuminaire efficiency is the ratio of light output emitted by the luminaire to the light output emitted by its lamps. Another way of looking at it: Luminaire efficiency is the percentage of light output produced by the lamps that are in turn emitted by the luminaire.Not all light produced by the lamps will exit the luminaire; some will remain trapped inside and dissipate as heat. The luminaires physical characteristics will affect how much light will exit and how much will be directed at the workplane.Luminaire efficiency is important because while you can have a very efficient lamp-ballast system, if the luminaire itself is not efficient at delivering lumens, then the lighting system overall is not either. Factors that affect the efficiency of the luminaire include its shape, the reflectance of its materials, how many lamps are inside the luminaire (and how close they are to each other), and whether shielding material such as a lens or louver is used to soften or scatter the light.While a high level of luminaire efficiency should be valued, overemphasizing it can lead to poor lighting quality and angry users. After all, a bare lamp offers 100 percent efficiency, but is hardly a good choice. In reality, the most efficient luminaires are often candidates for direct glare, particularly unshielded luminaires with direct distribution at lower mounting heights typically found in offices, classrooms and similar applications. In such cases, light may exit the luminaire very efficiently, but the luminaire itself is a glare bomb, and users are likely to resort to wearing baseball caps.Luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted or reflected from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square metre (cd/m2). A non-SI term for the same unit is the "nit". The CGS unit of luminance is the stilb, which is equal to one candela per square centimetre or 10 kcd/m2.Luminance is often used to characterize emission or reflection from flat, diffuse surfaces. The luminance indicates how much luminous power will be detected by an eye looking at the surface from a particular angle of view. Luminance is thus an indicator of how bright the surface will appear. In this case, the solid angle of interest is the solid angle subtended by the eye's pupil.IlluminanceIn photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of how much the incident light illuminates the surface, wavelength-weighted by the luminosity function to correlate with human brightness perception. Similarly, luminous emittance is the luminous flux per unit area emitted from a surface. Luminous emittance is also known as luminous exitance.[1]In SI derived units these are measured in lux (lx) or lumens per square metre (cdsrm2). In the CGS system, the unit of illuminance is the phot, which is equal to 10000 lux. The foot-candle is a non-metric unit of illuminance that is used in photography.Illuminance was formerly often called brightness, but this leads to confusion with other uses of the word, such as to mean luminance. "Brightness" should never be used for quantitative description, but only for nonquantitative references to physiological sensations and perceptions of light.The human eye is capable of seeing somewhat more than a 2 trillion-fold range: The presence of white objects is somewhat discernible under starlight, at 5105 lux, while at the bright end, it is possible to read large text at 108 lux, or about 1000 times that of direct sunlight, although this can be very uncomfortable and cause long-lasting afterimages.Incandesent LampsIncandesent Bulbs-Most commonly used.Least expensiveTheir soft, warm glow is reminiscent of candle light.Least efficient lighting source approx. 90% of the electricity goes into heat generation rather than light production.Bulbs convert power into light by passing electric current through a filament of tungsten wire. The wire consists of minicoils. The current heats the tungsten filament until it glows. The glass bulbs are filled with an inert gas mixture primarily of argon and nitrogen.The bulb can be clear, diffuse, tinted or coloured.It gives out attractive warm yellow light.Also called GLS General Lighting Service Lamp used for domestic purpose. Standard incandescent lamps last about 750 1000 hours.AdvantagesLow initial costCreates an inviting environmentImmediate startingEasily dimmedVariety of shapes,sizes and applicationsEasy to InstallDisadvantagesHigh operating costFragileShort lifeLow lumen per wattHigh heat outputHalogen BulbSlightly different shape & thicker heavier glass bulb. An incandescent lamp with a tungsten filament contained within an inert gas and a small amount of a halogen such as iodine or bromine. In ordinary incandescent bulb the filament evaporates over time & bulb wall blackens slowly as tungsten is deposited on it.The combination of the halogen gas and the tungsten filament produces a chemical reaction known as a halogen cycle which increases the lifetime of the filament and prevents darkening of the bulb by redepositing tungsten from the inside of the bulb back onto the filament.Fluorescent Lamps Introduction in 1938Aesthetically they are second class unpopular with interior designerWidely used because they are more efficient than incandescent lamps.Glass tubes coated on interiors with phosphor a chemical compound that emits light when activated by ultraviolet energy.Air in the tube is replaced with argon gas & a small amount of mercury is added.When f. lamp is turned on, the electricity heats cathodes at each end causing them to emit electrons, which in turn create an electric arc between the cathodes. The electrons in this arc collide with mercury vapour & argon or other gas atoms to produce invisible ultraviolet rays. These rays excite the fluorescent phosphor coating, producing visible light.Fluorescents are highly efficient because 80% of their light comes from the phosphor coating. BASIC COMPONENTS OF A FLUORESCENT LAMP BULB:usually a straight glass tube - can be circular, U-shaped, or curved .PHOSPHOR:coating inside the bulb that transforms ultraviolet radiation into visible light. The colour of the light produced depends upon the composition of phosphor.BASE:used to connect the lamp to the circuit & support it in the fixture.CATHODE:located at each end of the lamp. Cathodes are coated with a material that emits electrons & usually are made of coiled coil or single coil tungsten wire.GAS:argon or a mixture of inert gas at low pressure krypton sometimes is used.MERCURY:a minute quantity of liquid mercury is placed in the bulb to furnish mercury vapour. --------ReverberationReverberation is the collection of reflected sounds from the surfaces in an enclosure like an auditorium. It is a desirable property of auditoriums to the extent that it helps to overcome the inverse square law dropoff of sound intensity in the enclosure.Reverberation, in psychoacoustics and acoustics, is the persistence of sound after a sound is produced. A reverberation, or reverb, is created when a sound or signal is reflected causing a large number of reflections to build up and then decay as the sound is absorbed by the surfaces of objects in the space which could include furniture, people and air. This is most noticeable when the sound source stops but the reflections continue, decreasing in amplitude, until they reach zero amplitude.Reverberation is frequency dependent: the length of the decay, or reverberation time, receives special consideration in the architectural design of spaces which need to have specific reverberation times to achieve optimum performance for their intended activity.[3] In comparison to a distinct echo that is a minimum of 50 to 100 ms after the initial sound, reverberation is the occurrence of reflections that arrive in less than approximately 50 ms. As time passes, the amplitude of the reflections is reduced until it is reduced to zero. Reverberation is not limited to indoor spaces as it exists in forests and other outdoor environments where reflection exists.Echo of SoundIn audio signal processing and acoustics, an echo (plural echoes) is a reflection of sound, arriving at the listener some time after the direct sound. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room and an empty room. A true echo is a single reflection of the sound source. The time delay is the extra distance divided by the speed of sound. The word echo derives from the Greek (ch),[1] itself from (chos), "sound".[2] Echo in the folk story of Greek is a mountain nymph who loved her own voice. Animals that use echoes are cetaceans (dolphins and whales) and bats.Sound MaskingSound masking is the addition of sound created by special digital generators and distributed by normally unseen speakers through an area to reduce distractions or provide confidentiality where needed. The sound is broad band random that conveys no information about itself to a listener. It is often referred to erroneously as white noise or pink noise; the sound spectrum and level is specially shaped to provide the degree of privacy desired by occupants. Masking operates by covering up or masking unwanted sounds, similar to one-way windows that block the ability for a person to see persons behind them, or perfume that covers up other body odors. This is in contrast to the technique of active noise control which attempts to eliminate the unwanted sound. Sound masking is used in homes, commercial offices, medical facilities, court rooms, and in secure facilities to provide secrecy. It also can be used outdoors to restore a more natural ambient environment.Hearing Sensitivity of a human earThe human ear can respond to minute pressure variations in the air if they are in the audible frequency range, roughly 20 Hz - 20 kHz. It is capable of detecting pressure variations of less than one billionth of atmospheric pressure. As we get older, or exposed to loud sounds which damage our ears (such as loud rock concerts), the upper limit decreases.Sound IntensitySound intensity also known as acoustic intensity is defined as the sound power per unit area. The SI unit of sound intensity is the watt per square metre (W/m2). The usual context is the noise measurement of sound intensity in the air at a listener's location as a sound energy quantity.Sound intensity is not the same physical quantity as sound pressure. Hearing is directly sensitive to sound pressure which is related to sound intensity. In consumer audio electronics, the level differences are called "intensity" differences, but sound intensity is a specifically defined quantity and cannot be sensed by a simple microphone. Sound energy passing per second through a unit area held perpendicular to the direction of propagation of sound waves is called intensity of sound.Decibel ScaleThe decibel (dB) is a logarithmic unit used to express the ratio of two values of a physical quantity, often power or intensity. One of these values is often a standard reference value, in which case the decibel is used to express the level of the other value relative to this reference. The number of decibels is ten times the logarithm to base 10 of the ratio of two power quantities, or of the ratio of the squares of two field amplitude quantities. One decibel is one tenth of one bel, named in honor of Alexander Graham Bell; however, the bel is seldom used.The ear has the remarkable ability to handle an enormous range of sound levels. In order to express levels of sound meaningfully in numbers that are more manageable, a logarithmic scale is used, rather than a linear one. This scale is the decibel scale.Sound absorbants/Sound absorbing materialsAcoustic absorption refers to the process by which a material, structure, or object takes in sound energy when sound waves are encountered, as opposed to reflecting the energy. Part of the absorbed energy is transformed into heat and part is transmitted through the absorbing body. The energy transformed into heat is said to have been 'lost'.When sound from a loudspeaker collides with the walls of a room part of the sound's energy is reflected and part is absorbed into the walls. As the waves travel through the wall they deform the material thereof (just like they deformed the air before). This deformation has mechanical losses which convert part of the sound energy into heat through acoustic attenuation, mostly due to the wall's viscosity. The same attenuating mechanics apply for the air and any other medium through which sound travels.The fraction of sound absorbed is governed by the acoustic impedances of both media and is a function of frequency and the incident angle.Size and shape can influence the sound wave's behavior if they interact with its wavelength, giving rise to wave phenomena such as standing waves and diffraction.In general, soft, pliable, or porous materials (like cloths) serve as good acoustic insulators - absorbing most sound, whereas dense, hard, impenetrable materials (such as metals) reflect most.Threshold of PainSome sources quote 120 dB as the pain threshold and define the audible sound frequency range as ending at about 20,000 Hz where the threshold of hearing and the threshold of pain meet.The pressure at which sound becomes painful for a listener is the pain threshold pressure for that person at that time. The threshold pressure for sound varies only slightly with frequency and can be age-dependent. Additionally, people who have been exposed to more noise/music usually have a higher threshold pressure.Threshold shift can also cause threshold pressure to vary. Prolonged exposure to sound at levels evoking pain can cause physical damage, potentially leading to hearing impairment.The volume in acoustics refers to loudness. It is a common term for the amplitude of sound, the sound pressure level or the sound pressure. Different values for pain threshold pressure level and pain threshold pressure are found in the literature.Threshold of AudibilityThe minimum effective sound pressure of a specified signal that is capable of evoking an auditory sensation in a specified fraction of the trials; the threshold may be expressed in decibels relative to 0.0002 microbar (2 10-5 pascal) or 1 microbar (0.1 pascal). Also known as threshold of detectability; threshold of hearing.