In this paper, the relation between illuminance distribution on the desk, veiling reflection and visual fatigue is described.
The room chosen for the experiment was 2. 5 m by 3. 3 m by 2. 8 m high. A space ofthe visual task performance was illuminated by ceiling fittings and table lamps. Light sources were cool white fluoresent lamps and incandesent lamps. The illumination levels were adapted for the performance of visual tasks from 300 lx to 700 lx on the surface of the visual task chart.
The visual task consisted in the recognition of small Landolt's rings of 2. 5 mm diameter printed with black ink of 3% reflectance on the mat white paper (90% reflectance) or grossy paper (90. 5% reflectance). Besides, the subject read the books as visual task. The task time was limited to 80 minutes or 120 minutes.
The degree of the visual fatigue was estimated with the fluctuation rate of the accomodation time of the eye during the visual task performance.
The following results are obtained:(1) Generally, the more uniform the illuminance distribution, the less the increase of the eye fatigue.
(2) In order to decrease the eye fatigue by the veiling reflection, good lighting methods on the desk is to locate the ceiling fittings in the position out of specular reflected zone.
(3) The eye fatigue is most remarkable under the local lighting by only the table lamp. The eye
fatigue under the locallighting used together general lighting is remarkable as compared with that under the general lighting.

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The lighting and daylighting designs of a room often include a prediction of the average illu minance on the working plane, and the illuminance or luminance distribution on various surfaces. It is very difficult to obtain an analytical solution of various interior inter-reflection problems which is based on the Fredholm type integral equation.
In this paper, the authors have accomplished a program of FORTRAN IV for the numerical solution based on the photometric quantities by using the point-by-point method, the luminous flux transfer method and the superposition theorem in an idealized room. It is possible to predict the direct and total flux received by a rectangular surface, and the average illuminance, and the illuminance distribution by using this program, and moreover to predict an isolux diagram on the horizontal or vertical plane from the output of the digital computer such as the line printer or X-Y plotter.

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[in Japanese]

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