A new formula is proposed for evaluating discomfort glare from large glare sources with uniform luminance. The formula has four parameters: luminance of the glare source, size of the glare source, background luminance and position index. An experiment was conducted to investigate the effect of each parameter on the evaluation of discomfort glare. Twenty subjects evaluated discomfort glare from the model window. The new formula shows the relation between the degree of discomfort glare and the parameters. The formula is distinct from other formulas in that it has a simple form and the background luminance has little effect on the degree of discomfort glare. It is expected that discomfort glare from large glare sources with uniform luminance can be appraised using the formula.
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