Factors affecting the quality of lighting

Glare causes discomfort or impairment of vision and is usually divided into three aspects, i.e. disability glare, discomfort glare, and reflected glare. 

It is referred to as disability glare if it impairs the ability to see clearly without necessarily causing personal discomfort. The glare caused by the undipped headlamps of an approaching car is an example of this. 

Reflected glare, which can be disability glare or discomfort glare, is the effect of light reflected from a shiny or polished non-matt surface. The visual effect may be reduction of contrast, or distortion, and can be both irritating and, in certain workplaces, dangerous. 

For many years in the UK, a glare index system has been in use for quantifying the effects of direct glare. It is also in use in certain other countries. 

This is now being replaced by the international Unified Glare Rating System (UGR) which has been adopted as standard in Europe. The numerical values will normally be much the same but the derivation formula is different  

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