Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . imaginary sphere. Evidently the density of the normalillumination against the inner surface of the sphere will bear tothe illumination of the circular surface source the inverse ratio ofthe interior area of the exposed zone of the sphere to the area ofthe lighting source, since the lumens produced must equal thoseutilized. This ratio equals the square of the ratio of the radiusAC to the diagonal AD; when the radius of the circular source istaken as the unit of length for the measurement of all d
Light, photometry and illumination : a thoroughly revedof ''Electrical illuminating engineering'' . imaginary sphere. Evidently the density of the normalillumination against the inner surface of the sphere will bear tothe illumination of the circular surface source the inverse ratio ofthe interior area of the exposed zone of the sphere to the area ofthe lighting source, since the lumens produced must equal thoseutilized. This ratio equals the square of the ratio of the radiusAC to the diagonal AD; when the radius of the circular source istaken as the unit of length for the measurement of all distances. 222 LIGHT, PHOTOMETRY AND ILLUMINATION and the unit of illumination is taken as the surface brilliancy ofthe source, then the percentage value of the illumination on theinterior of the sphere is equal to 100, divided by the square of thediagonal AD. For convenience any sphere passing through the edges A andB, as just indicated, can be referred to as an equilux spheres of the proper sizes being employed, one isenabled to explore the whole region illuminated by the source. 10 11 12 13 14 16 Fig. 126.—Equilux spheres. and to ascertain immediately for any desired point within thespace explored the exact value of that component of the lightflux which is normal to the particular equilux sphere passingthrough that point. In Fig. 126 are indicated numerous equilux spheres and thepoints of intersection of these spheres with horizontal planes(floors) at distances of units and 7 units of length (radii)below the light source, and with vertical planes 3 and 5 length-units distant from the center of the source. Illumination on Horizontal Planes.—(McAllister, Ref. Cit.)Intersections of the two assumed horizontal planes (floors) withthe equilux spheres are shown in Figs. 127 and 128; evidentlythe points of equal illumination lie on circles having as the com- ILLUMINATION CALCULATIONS 223 mon center the point on the floor immediately below the centerof the circu
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectlight, bookyear1912
