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Convert between lumens per square foot and other major units of illuminance.
The unit of luminous flux in SI. Symbol, lm. One lumen is the luminous flux emitted within a solid angle of 1 steradian by a point source with an intensity of 1 candela. In terms of base units, the dimensions of the lumen are candela × steradian.
The lumen existed with different definitions prior to SI.¹
A typical use for the lumen is to describe how much light ordinary household light bulbs give off. The packaging usually gives the bulb's light output in lumens; a new 75-watt incandescent bulb puts out about 1,180 lumens.
1. Parry Moon.
System of photometer concepts.
Journal of the Optical Society of America, volume 32, number 6 (June 1942).
Page 355: “The lumen was proposed by Blondel in 1894 and is now universally accepted.”
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Last revised: 11 September 2002.