A method for evaluating discomfort glare from windows: Part 2. Discomfort glare from large glare sources with non-uniform luminance

A new formula is proposed for evaluating discomfort glare from large glare sources with non-uniform luminance. Three types of experiments were conducted using a modal window divided into two parts. Each part of the window had different luminance. First, the luminance ratio was measured when the observers perceived the difference of luminance between the two parts. The result of the measurement shows that the difference of luminance can be perceived when the ratio is 1:1.24. In the second experiment, the window was divided into two parts of the same size, and the degree of discomfort glare from the window was investigated. In the third experiment, the same test was conducted, but the window was divided into two parts with different size. The degree of discomfort glare was calculated using two methods. One used the average luminance of the window as a parameter, and the other summed up the degrees of discomfort glare from both parts of the window. There were no significant differences between the two methods. Consequently, a formula that uses the average luminance is proposed for evaluating the discomfort glare from large sources with non-uniform luminance.