Abstract
It is effective for power-saving of office lighting to set working plane illuminance lower than usual, but without consideration of room appearance this tends to lead to gloomy impression. To avoid this negative effect, some methods to predict brightness impression are used for office lighting design, but they have not been well examined from the view point of applicability to office lighting. It is apparent that the average luminance of office perspective image is important but the value changes in accordance of view range. This study, as a basic research, examined appropriate vertical range for prediction of perceived spatial brightness.
The authors set 48 different luminance distribution conditions in a 1/6 scale model of office environment, and asked the subjects to evaluate spatial brightness with magnitude estimation technique. The luminance distribution from the subjects' evaluation point was measured by a digital camera with 180 degree fish-eye lens and average luminance was examined.
As the result, the authors obtained followings;
1) When sitting on a desk seat, spatial brightness can be predicted by mean luminance ranging from 0 to 20 degrees on the luminance image in vertical, with exclusion of objects just around the desk like partitions, but in the case of short room depth or including windows, the mean should be ranging from 0 to 40 degrees.
2) Vertical range to average luminance for prediction of spatial brightness should be adjusted in accordance with characteristics of the room examined.
