Illuminating Engineering Society, Association of Public Lighting Engineers (Great Britain) · [London] · leaf 112
to examine into the value of thelight emitted in certain directions by thebulb. Imagine the light to be divided THE ILLUMINATING ENGINEER (apbil 1921] lol up by a series of cones having semi-vertical angles of 10°, 20°, 30°, etc., andhaving a common axis, namely the axisof the bulb and lamp as… … Fig. 4. A reduction in the effective diameter ofany given lamp by, say, a disc with acircular hole cuts off some of the light,but a similar reduction to the same final to project, say, 70 per cent, of the spheri-cal candlepower forward, while a 12 in.lamp of greater focal Length and…
Lighting
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