Tutorial | Design of lighting schemes
The following factors are considered while designing the lighting scheme:
1-Illumination level: This is the most vital factor because a sufficient illumination is the basic means by where we are able to see our surroundings; it is the task of illumination to give objects a distributed brightness. Objects which are seen for longer duration of time require more illumination than those for casual work. Similarly moving objects require more illumination than those for stationary object.
2-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 eve 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 in addition to localized lighting. Apart from the consideration of causing fatigue, local lighting without using matching general lighting creates psychological feeling of loneliness, gloom and unfriendliness. The modem trend is thus towards "localized lighting plus general lighting" and towards the adoption of general lighting oriented towards the working surface" especially in mass production factories, offices, drawing offices, shops etc.
3-Color of light: The appearance of the body color entirely depends upon the color of the incident light. In general the composition of the light should be such that the color appears natural i.e its appearance by artificial light is not appreciably different from that by day light.
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4-Shadows:
In lighting installations, formation of long and hard shadow causes fatigue of eyes and therefore is considered to be a short coming. Complete absence of shadows altogether again does not necessarily mean an ideal condition of lighting installations.
5-Mounting height:
The mounting height will largely be governed by the type of building and type of lighting scheme employed. In the case of direct lighting, in rooms of large floor area, the luminaries should be mounted as close to the ceiling as possible.
Lowering them not only will make the illumination less uniform, but will also bring them more into the field of vision, thus increasing the glare, without causing an appreciable increase in the coefficient of utilization. In the usual case of small rooms with high ceilings, there is something to be gained by lowering the luminaries.
6-Spacing between luminaries:
Correct spacing is of great importance to provide uniform illumination.
With fluorescent luminaries it is good practice to aim at a value of unity for this ratio, and to set an upper limit of ¾ In this case of tungsten lamps combined with focusing reflectors, it is good practice to aim at a horizontal spacing between rows approximately equal to the height of the ceiling above the working plane, and in no case should the horizontal spacing exceed 1 ½ times this height.
height of the ceiling above the working plane, and in no case should the horizontal spacing exceed 1 ½ times this height.
7-Color of surroundings walls:
The illumination in any room depends upon the light reflected from the walls and ceiling. White walls and ceiling reflect more light as compared to colored ones.
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