: the candlepower of an extended source of light that is equal to the candlepower of a point source of light which if located at the extended source would produce an equivalent illumination at the distance specified
The inverse square law is not correct at short distances. This does not affect the calculations for efficiency or utilization. In fact, the apparent candlepower reported for a ten-foot test distance is more realistic for actual installations than that measured at 40 feet.—Illuminating Engineering, 1962
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