視線近傍の小さなグレア光源による等価光幕輝度

Abstract

A reduction of visibility caused by a glare-source can be expressed by an “equivalent veiling luminance”. The relationship between the reduction in visibility and the size of the glare-source is not clearly understood when the glare-source size is less than 1 degree. The equivalent veiling luminance has also been studied insufficiently for small values of angle θ which the glare-source makes with the line of vision. A visual experiment was carried out to clarify these properties. In this experiment, a circular glare-source of diameter 3 to 27 minutes was presented near the line of vision of an observer. Landolt rings were employed as test objects on a screen panel.The results show that not only the luminous intensity of the glare-source but also its area S has an effect on the reduction of visibility for a relatively small glare-source. The equivalent veiling luminance varies approximately with θ-2.4 and S-0.23. However, beyond a certain value, area does not affect the reduction very much in the case of high backgroud luminance. The apparent luminance contrast of the Landolt ring, when the visual acuity is reduced to half, is constant regardless of the background luminance of 1 to 100 cd/m2.