It is important to create preferable atmosphere of luminous environment as well as to satisfy visibility of visual tasks on a working plane such as desk tops, to make comfortable office lighting.
To make preferable luminous atmosphere, it is required to achieve preferable luminous balance between main surfaces such as visual tasks and other room surfaces.
Series of experiments with subjective appraisals were carried out to clear preferable range of luminous balance in the office room.
At first in this report, preferable illuminance of the front wall related to the illuminance of the visual task on the desk is reported.
Results are as follows:
(1) Optimum wall illuminance Ew is given in the following experimental formula.
log E_w=(0.27logr+0.73) log E_D-1.llogr+0.43
Where E_D: illuminance on the desk
r: reflectance of the front wall
(2) For the guide of a usual lighting design, permissible range of wall illuminance is found to be 320-440 lx, when illuminance on the desk is choosen freely or varied as a design between 500-1000 lx, and also wall reflectance is choosen freely between recommended range of 0.3-0.8.
Here “permissible range” means not necessary optimum but in between both limits of upper and lower and is regarded as to be recommended.
This results may be widely applicable to a comfortable lighting design of a usual office room.