Lighting quality criteria
The five conditions that need to be satisfied (in order for the eye to perform properly), are that:
• The detail must be of a certain minimum size.
• The detail itself should have a certain minimum luminance to reveal its shape and texture.
• The eye must be adapted to the overall luminance in the field of view and luminance distribution such that proper adaptation is possible. In other words: there must be no excessive glare.
• The detail to be observed must have a certain minimum contrast with respect to the surroundings in general. This is a combination of brightness and color contrasts.
• The object must be presented for viewing for a certain minimum period of time
Provided the above visual requirements are satisfied, details of the object in question will be perceived by the eye. But the lighting must permit more than mere perception: it must be such as to allow the eye to perform its task with the least possible chance of error and with the minimum effort and stress.
Principal lighting criteria
This leads us on to a consideration of the five principal lighting criteria:
• lighting level
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• freedom from disturbing glare
• spatial distribution of the light
• color appearance and color rendering
The above criteria hold for daylight as well as for artificial lighting or a combination of both.