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Lumens (or luminous flux), simply put, is a measurement of light that takes into account that varying sensitivity of the human eye to different wavelengths or colors of light. This differs from radiant flux, a measurement of total light emitted, which can be in the infrared and ultraviolet spectrum (wavelengths that the human eye cannot perceive).
The lumen is defined in relation to the candela by
1 lm = 1 cd•sr
That is, a light source that uniformly radiates one candela in all directions radiates a total of 4π lumens. If the source were partially covered by an ideal absorbing hemisphere, that system would radiate half as much luminous flux—only 2π lumens. The luminous intensity would still be one candela in those directions that are not obscured.
In simpler terms, a lumen is a measurement of light. One lumen is equal to the amount of light that 1 candle will emit on 1 square foot, 1 foot away from the flame. 1 lumen = 1 foot candle |
