lumen

For the meaning of any metric prefix, go here.

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.ยน

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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