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This true-area development of a hemisphere is used to plot the distribution of intensity of radiation about a lighting unit. The curves shown are isocandles or lines of equal intensity.
This is the familiar projection of a hemisphere used in map making and it has distortions of areas that limit its use for engineering purposes. The data curve is shown in two positions 60 degrees apart. The chart here described is intended to facilitate such a transfer without computations, or the use of a distorted-area web.
The details of changing a spherical projection of the type of Fig. 2 into a projection having the property of representing equal angles by equal straight lines is here outlined.
This chart is a working model of Fig. 3(d), with changes in scale to improve its accuracy and convenience of use.
These isocandles are the same curves as those of Fig. 1, but they have been rotated counterclockwise through 60 degrees. Since the shapes are changed, the curves must be rotated point by point.
The plotted curves represent the traces of cones from the light center to boundaries of various zones of a composite form of floodlighting reflector. Radiation in the region above curve
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