CIE 117

The task of the CIE Technical Committee TC 3-13 was to produce a practical discomfort glare evaluation system. The Unified Glare Rating (UGR) formula described in this technical report, combines features of the Einhorn and the Hopkinson formulae and incorporates the Guth position index. It may be regarded as being composed of the best parts of the major formulae in terms of practicability and of familiarity with the results of glare prediction. The formula recognises the effects on the glare index of observer position and direction of view. The report also describes, in the appendices, a tabular method, which uses reference values and standard conditions, allowing the production of simple tables, similar to those for utilisation factors, for use in luminaire data sheets. A rough estimate of discomfort glare is given by the luminance limiting curve (UGR curve) method. The appendices also show how the curves can be constructed and used. The report recommends a practical CIE discomfort glare evaluation system for use in the next edition of the CIE Guide on Interior Lighting.