In this paper the author describe, the-results of tests to obtain the spherical reduction factors of theincandescent tungsten lamps of various types.
In the first place he considers the effects of bulb sizes and then the frosting of bulbs upon the valuesof the spherical reduction factors. Then he treats the actual data on the lamps of the present manufacturenot only for the 100 volt type but also for 200 volt and 50 volt types.

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For incandescent lamps the temperature distribution surrounding the lamps may affect considerably thelife of lamps and socket insulation which operate. On this reason we measured some temperature distributionon the bulb surface and socket at practical illuminating arrangement changing Shades and inclination of theboth to the vertical line. The ou measurements are as follows.
1. Vacuum tungsten lamp bulb surface temperature distribution.
2. Gas-filled lamp bulb surface temperature distribution
3. Change of temperature distribution with shades.
4. Change of temperature distribution with relative position of bulb and shade.

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Light sources for natural lighting can be taken to be of uniformly bright surfaces, and therefore thedirect illumination can be calculated by the method proposed by the author previously and the diffusedillumination can be obtained easily. As the extension of the method, the author proposes a diagram of solid angle projected. The radius vector of the diagram is R sin 0 and the polar angle is the horizontalangle, where R is the radius of the diagram and 0 is the incident angle. Then if we plotj the contourof the light source on the diagram, the area of the diagram gives the illumination at that point.
Using the projected angle diagram with meridians which represent the time of the day, we can solvethe various problems of the orientation of the window.

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