This paper deals with characteristics of the illuminance and the shadow factor within a shadow affected by reflected light, in an infinite length room which has a ribbon-shaped light source and a column (a shadow caster) of infinite length.Calculations are done by Monte Carlo method which is widely used lately to predict'the illuminance distribution of a room. First, Monte Car[o method for numerical calculations is presented to obtain the illuminance within a shadow. Next, some experiments are made under the same conditions as the calculations. And, the experimental results are compared with the calculated results. As there is not a large difference seen between them, it is confirmed that the above method is suitable.Finally, the characteristics of the illuminance and the shadow factor on the floor at the varied reflectances of the room surface and the shadow caster are obtained and examined.

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