Experimental study on preferable luminous balances in an office room using with the local lighting

Abstract

It is important to create the proper luminous balance between main surfaces such as visual tasks and other room surfaces, as well as to satisfy visibility requirements for visual tasks on a personal working plane such as desk tops. The overall effects create comfortable office lighting.
Recently task and background lighting techniques are often used. This system consists of general lighting providing low standard illuminance, and local lighting providing higher level illuminance on the desk to satisfy the visibility requirements for visual tasks.
A series of experiments with subjective appraisals were carried out to clarify a preferable range of luminous balance in the office room, that is recommendable illuminance of the front wall and the surrounding desks, comparing to the illuminance of the visual task area on a desk.
The experiments' results are as follows:
(1) As a guideline for a typical lighting design, permissible illuminance range of the surrounding desks should be 270-500lx, and the wall illuminance should be 260-540lx, when illuminance of the visual desk is 700lx, and wall reflectance is choosen freely between 0.3 and 0.8.
Here ‘permissible illuminance range’ doesn't mean optimum but between upper limit and lower limit of recommended condition.
(2) When illuminance on the desk is choosen 500 and 1000lx freely or illuminance varies locally in the room, permissible illuminance range of the surrounding desks should be 270-500lx, and the wall illuminance should be 260-540lx.
These results may be widely applicable to a comfortable task and background lighting design of a typical office room.