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Evaluation of the effect of daylight on room brightness

The purpose of present study is to investigate effects of daylight on room brightness using a reference matching method. Participants observed two scale models simulating a room. One was a test room with a window through which artificial daylight entered and the other was a reference room without a window. Participants made brightness match by adjusting illuminance of the reference room with various illuminance levels (from ceiling luminaires) of the test room and window sizes. The results showed that, at the illuminance levels below 300 lx, the illuminance adjusted by participants was low even if the daylight increased the total illumiance of the test room. However, the adjusted illuminance increased efficiently with the daylight at the 1000 lx illuminance level. These results suggest that effects of daylight on brightness change with illumiance levels. The results were also discussed in terms of those of previous study using a magnitude estimation method. INTRODUCTION Recent development of lighting design and technology has enabled us to create various visual environments easily. Consequently, however, many designers and researchers have been faced with problems, not usually considered in previous studies. For example, although illuminance is used as an index of room brightness, a low illuminance room sometimes appears brighter than a high illuminace one. This fact not only indicates that illuminance does not always reflect room brightness accurately, but it also leads researchers to investigate factors which causes discrepancies between illuminance and brightness. One of such factors is daylight coming from windows. A few studies examined effects of daylight on room brightness [1] and found that increases in illumiannce by daylight did not sufficiently enhance room brightness, as compared with that by a ceiling light, particularly in the low illumianance room condition. In the present study, we further investigated the effects of daylight on room brightness by using a reference matching method. In this method, participants were asked to adjust illuminance of the reference room with various illuminance levels (from ceiling luminaires) of the test room and window sizes. EXPERIMENTAL METHOD In the present study, two 1/8 scale models simulating an office room were used (width; 800 mm, length; 1,200 mm, height; 340 mm). Figures 1 and 2 illustrate experimental apparatus and interior appearance. One room had no window and served as a reference room. Another room had a window and served as a test room. In both rooms, achromatic furniture and interior were arranged. To simulate daylight, we used 8 fluorescent lamps attached outside the test room. By changing the number of lamps turning on, the intensity of simulated daylight was manipulated: High (8 lights), Middle (4 lights), Low (2 lights), and Very Low (1 light). The illuminance of test room from ceiling luminaires and the window size were also manipulated. The Illuminance of the test room was either 100, 300 or 1000 lx. The window size was either full-window, 1/2, 1/4 or 1/8. The O B 43