Lighting
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Workstation light level
The effective lighting on a work surface is the sum total of all the light
rays striking the surface, including rays directly from lamps and reflected
from walls or other objects in the room. Usually, the source document is the
critical factor in determining how much and what type of light should fall
on the work surface. White paper has a reflectance factor of about 70% to 80%.
This means that if the desired brightness of the paper is 100 cd/m2,
the intensity of the light falling on the paper should be about 400 lux. With
a paper of a much lower reflectance, for example, colored paper, the ambient
light would have to be increased to achieve the same result. An average light
level of about 400 lux (or slightly less) is usually satisfactory for office
environments. Most home lighting tends to run about 50 to 100 lux.
Ambient light levels are not as important when only reflective surfaces are
considered. For example, if a piece of paper on a desk has a reflectance of
70% and the desk top has a reflectance of 10%, the ratio of paper brightness
to background brightness is 7:1, regardless of the ambient lighting. A VDT
on the other hand, generates its own light to create the informationcarrying
image on its surface. Although there is a range of adjustability for the image
brightness of a VDT, the range is limited and does not automatically alter
with changes in the ambient illumination. If these differences, along with
environmental conditions, are not considered in the design of the workstation,
then some visual discomfort may be encountered.
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