Experimental study on the necessary illuminance of human faces in an office room

Abstract

It is important to satisfy the visibility needs of visual tasks on a working place (such as a desk top) as well as to make comfortable office lighting.
Visual tasks may include desk top work, VDT work or even talking to another person, in which case, the face of the person becomes a visual task surface.
A series of experimental studies, with subjective appraisals, were carried out to clarify a preferable face illuminance against background wall illuminance in an office room, especially while using task and ambient lighting (general lighting with a local lighting on a desk top).
In this experiment, background wall illuminance against an illuminance on the desk, is set at a lower limit value for nearly 90 percent of observers, and the face illuminance is adjusted by the obsever.
The experiments' results are as follows:
(1) Preferable face luminance against the background wall luminance can not be expressed simply.
(2) For a plan of task and ambient lighting in the office, it is desirable to have a preferable range of face illuminance for illuminance on the desk top on condition that wall illuminance is fixed.
As a guideline for typical lighting design in the office, an optimum illuminance range for the face should be 450-6201x; for an illuminance of the desks: 7501x, and minimum illuminance range for walls should be 270-3001x; for an illuminance on the desk: 1000 lx, on condition that preferable range of illuminance on the desk top should be 750-1000 lx and wall reflectance is 0.3-0.8.