BS EN 12464-1 : 21

Glare is an unpleasant sensation produced by bright areas within the visual field. These could be surfaces, parts of luminaires, windows and/or roof lights, viewed directly or via reflections.

Glare is not desirable and should be limited. In the workplace, it can be experienced as discomfort glare or as disability glare, at the same time, or separately. In indoor workplaces disability glare is usually not a major problem if discomfort glare limits are met.

Discomfort glare

To select a luminaire suitable for given space the rating of discomfort glare caused directly from the luminaires shall be determined using the Unified Glare Rating ( UGR) method. The UGR value of the lighting installation shall not exceed the value in the tables. The series of UGR is 16,19, 22, 25, 28, where the lowest value is required for more detailed work. 

All assumptions made concerning luminaires, room dimensions, room surface reflectance and spacing and height ratio in the determination of UGR shall be stated in the project documentation.

A new informative annex to the standard describes the recommended procedure for the application of UGR in ‘unusual’ situations. There are further details on the procedure – for example, for unusual luminaire sizes, irregular surface shapes and arrangements of fittings – as well as deviating degrees of room reflection.