In recent years, the Unified Glare Rating (UGR) as recommended by the CIE has become widely accepted as a general formula for assessing glare. The formula is given below:
The background luminance can simply be derivedfrom the illuminance at the eye of the observer:
This formula is requires the prior knowledge of the position and brightness of each potential glare source. It is quite accurate but relatively difficult to work with. It is best used from within some computer software. For artificial light sources, such packages exist from most major producers of light fittings. They all require the modelling of the scene under investigation and produce a glare index for a defined postition within the room.
|Working area||Maximum allowed UGR|
|Industrial work, fine||22|
|Industrial work, medium||25|
|Industrial work, coarse||28|