[8.6] A curve, often polar, that represents the variation in luminous intensity of a lamp or luminaire in a plane passing through the light center.
Note: A vertical candlepower distribution curve is obtained by taking measurements at various angles of elevation about a source in a vertical plane through the light center; unless the plane is specified, the vertical curve is assumed to represent an average such as would be obtained by rotating the lamp or luminaire about its vertical axis. A horizontal intensity distribution curve represents measurements made at various angles of azimuth in a horizontal plane through the light center.
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