A comparison of the accuracy of methods of calculating the IES glare index

Abstract

Calculations of the IES glare index have been made by three methods over three sets of conditions: (a) the full glare index method as described in IES Technical Report No. 10; (b) a simplified method devised by Lowson and later extended, and (c) a circular slide rule technique based on the extended and simplified approach. The three sets of conditions were chosen at random from a limited range of conditions. Comparisons were made between the glare indices calculated by the full method and the simplified method. It was concluded that the probability of obtaining a difference of ±1-0 was very small (<0-01); no evidence was found to suggest that the differences tend to increase at extreme conditions. It is concluded that in conditions where all the methods are available the simplified and less time-consuming method can be used without incurring any penalty in accuracy.