Good lighting of places of work, streets and roads is necessary for proper visibility. Lighting should neither be strong nor dim. Bad lighting may lead to eye strain, headache, irritability, loss of temper and accidents.
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In industries inadequate lighting is uneconomical as the output tends to decrease and the accident rate might increase. Strong or bright lighting may produce glare which is dangerous to the eyes and decreases critical vision. The source of light should emit uniform light that means it should not flicker.
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The distribution of light must be uniform over the whole area of work. There should be no shadows in the field of work as it may interfere with vision. No worker should be allowed to gaze directly at a bright light and every effort should be made that glazing light does not enter the eye.
As far as possible fluorescent lighting should be provided as it is economical because less electricity is consumed by them, avoids shadows and provides cool and efficient lighting therefore helps in increasing the efficiency of workers.
Lighting may be natural or artificial. Natural lighting is derived from the sunlight. The buildings and rooms usually get the reflected light from various objects or reflected light from the sky. Intensity of natural lighting depends on the time of day, season and weather.
Wherever possible natural lighting should be used because it is economical and has beneficial effects on health as the sun rays contain light rays, heat rays and ultraviolet rays. Moreover it does not cause any pollution. In planning the natural system of lighting the following points must be taken into consideration:
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(i) The objects which obstruct the light should be removed partly or completely.
(ii) Proper windows regarding their location, number, size and shape should be provided.
(iii) Too many screens and curtains obstruct the natural light.
(iv) All glazings and window panes should be kept clean.
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(v) Rooms should be regularly white-washed rather than colour washed because white washing provides better reflection of light.
We cannot depend upon natural lighting all the time i.e. during nights and cloudy days we will have to use some artificial lighting system. Common sources of artificial lighting include candles, kerosene lamps, gas lighting and electric lighting. Out of all these systems electric lighting is more commonly used now a day.
Electric lighting does not involve combustion and therefore no oxygen is taken and no waste substances are produced. Candles are used for lighting in emergencies only as they are harmful because their flame is naked and sooty and they are costly. Kerosene lamps are also not very favoured for lighting.
Various types of vapour lamps are being used. The neon filled sodium discharge lamp gives out monochromatic yellow light which is quite suitable for highways. Generally tube-lights are more commonly used these days because they consume less electricity hence economical, provide cool and efficient lighting. Use of direct lighting as in the case of table lamps projecting towards working area should be avoided as it may cause eye strain.
It should be used only when very fine work is to be done. Indirect light is good for illumination. The light is directed towards ceiling or upper parts of the wall and from there the light is reflected to the working area.
Intensity of artificial light is measured in terms of foot candles. A foot candle is the intensity of light received at a point which is placed at a distance of one foot from the source of light of a standard candle power.
A standard candle weighs 75.6 gms and burns 7.2 gms of wax per hour. The electric unit ‘watt’ is equivalent to 0.88 candle power. A minimum of six foot candles illumination is required for clear visibility.
For continuous reading it should be 10 to 15 food candles. The intensity of day light is not measured in terms of foot candles but in units called ‘Daylight Factor’ (D.F.). This is measured by a special instrument known as daylight factor meter. For clear visibility at least one percent daylight factor should be present in rooms.