This study proposes clues to control the luminance contrast between windows and the walls around them.
Until now, the idea of incorporating daylight to save energy has been the mainstream, but in recent years the "right to receive daylight" has been reviewed in light of the impact on circadian rhythm. However, as has been conventionally recognized, taking direct sunlight directly into the room produces extremely bright areas. Even if the window is not exposed to direct sunlight, the brightness of the sky and surrounding buildings may cause glare, which reduces visual comfort. In addition, even if glare does not occur, if the contrast between the outdoor and indoor brightness seen through the window is large, the impression of the room will be darkened. It is not desirable to have too much or too little daylight. Especially in the visual environment, it is very difficult to adjust it, and appropriate control is required.
There are daylight factor and glare index (eg PGSV) as clues for daylight control. However, the former is only a guideline for the amount of light that should be guaranteed in daylight, and it cannot be said that visual comfort can be guaranteed. The latter can predict the degree of glare, but it is not clear how much glare is acceptable. Previous studies by the authors have shown that interior reflectance changes the required level of spatial brightness. As with spatial brightness, glare may have different tendencies in perception and demand, so this study examined the effect of interior reflectance.
Experiments are conducted in full-scale space, and the main variables are interior reflectance, blind slat width and angle. The size of the window is strictly different because the space used for each experiment is different, but it is about 1m x 2m and is installed at waist height. Windows were prepared both artificial uniform luminance and natural sky. Subjects are men and women in their 20s.
From the experimental results, the following became clear. First, glare standards are set according to visual task, but this study shows that the degree of glare tolerance tends to differ depending on the interior reflectance. This does not mean that the perception of glare is different, but that the permissible degree depends on the interior reflectance. Next, when calculating the luminance contrast between the window and the surrounding walls, the conditions for windows with blinds were also examined. It was thought that the maximum luminance and the non-uniformity of luminance had an effect, but these effects were not detected, and it became clear that the average luminance in the window area could be sufficiently explained. On the other hand, in the case where the high-luminance part such as the sky and the low-luminance part such as planting are clearly separated in the window area, the average value of only the high-luminance part is better than the entire window area.
Based on the experimental results, the formula "75% AIL " was proposed. The equation includes the brightness of the window and the internal reflectance. The correlation coefficient is R = 0.98.
By using this relationship, it is possible to control the window luminance and the output of artificial lighting, but the size of the window and other factors are limited in experimental conditions, so further studies are required.
