Light

Light

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  Vd Rakesh Shukla Lecturer, Deptof Swasthavritta GAAC, AhmedabadVd Rakesh Shukla, GAAC, Ahmedabad 1
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  *Good lightning isessential for efficient vision *For efficient vision, the following factors are essential 1. Sufficiency: light should be sufficient enough for vision without strain. Illumination of 15-20 foot candles is minimum requirement , it ranges from 5-100 foot candles. 2. Distribution: light should be uniform and of same intensity.Vd Rakesh Shukla, GAAC, Ahmedabad 2
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  3. Absence ofglare: glare is excessive contrast. The best ex. for glare is automobile headlight at night, the same light at day time would not cause glare due to absence of excessive contrast. 4. Absence of sharp shadows: slight shadows are inevitable, but sharp and contrasting shadows lead to confusion. 5. Steadiness – source of light should be constant and non flickering. Flickering may cause eye stain and accidents. 6. Color of light: is not so important as long as the intensity is sufficient. The artificial light should be as near to natural light. 7. Surroundings: color contrast is necessary and roofs and ceilings should have reflection factor.Vd Rakesh Shukla, GAAC, Ahmedabad 3
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  Natural lighting *It isderived partly from the visible sky and partly from reflection. Lighting in the room is by the reflection of light colored objects. *It also depends upon the time of the day, season, weather and atmospheric pollution. Since natural light is accompanied by radiant heat all attempts to eliminate it should be made. Vd Rakesh Shukla, GAAC, Ahmedabad 4
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  Improving day lightillumination 1) Orientation – the illumination varies in buildings facing in east or west direction, direct sunlight may heat up the room especially in summer season. 2) Removal of obstructions – removal of obstructive items partially or wholly does give effective lighting. 3) Windows – tall windows gives greater penetration of light; broad window gives greater diffusion of light. 4) Interior of the rooms – ceilings should be white, upper portions of the wall light tinted, lower portions some what darker. This provides comfortable contrast. Vd Rakesh Shukla, GAAC, Ahmedabad 5
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  Artificial light Day lightmay not meet with the requirement of illumination always especially during cloudy days. Artificial light should be as close to daylight in composition. There are 5 systems of artificial lighting 1) Direct lightings – 99-100% of light falls over work area. It is efficient and economical but tends cast sharp shadows. 2) Semi-direct – 10-40%light is projected upwards so that it is reflected back on the object by the ceiling. Vd Rakesh Shukla, GAAC, Ahmedabad 6
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  3) Indirect: lightdoes not strike a surface directly, because 90-100% of light is projected upwards towards the ceiling and walls. This give general illumination of the whole rooms and not of any object. 4) Semi-indirect: 60-90%of light is directed upwards, and the rest downwards. 5) Direct-indirect: light is distributed equally. Vd Rakesh Shukla, GAAC, Ahmedabad 7
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  Methods of artificialillumination Filament lamps: the electric current heat up the tungsten filament and the light emitted depends upon the temperature, hotter filaments produce bluer light. Accumulation of dust on the bulbs reduces illumination by 30 – 40 %. Fluorescent: the lamps consist of a glass tube filled with mercury vapor and an electrode fitted at each end. The inside of the tube is coated with fluorescent chemicals, which absorb practically all the ultra violet radiations and remit the radiations in the visible range.Vd Rakesh Shukla, GAAC, Ahmedabad 8
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  Biological effects oflight The observation that day light could cause the in vitro degradation of bilirubin is now being used as a therapeutic measure in premature infants with hyperbilirubinemia. (Photo therapy) Other biological effects include biologic rhythm of body temperature, physical activity, stimulation of melanin synthesis, activation of precursors of vitamin D, adrenocortical secretions and food consumption. Vd Rakesh Shukla, GAAC, Ahmedabad 9
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