In the Spotlight #6: Lumens, Luminous Flux, and Luminance
Recently a customer asked what the difference between lumens, luminous flux, and luminance was. I thought this was an especially good question and should be addressed as all three of these terms of measure are used in technical specifications, and sometimes even all at once! Lumens and luminous flux should be tackled first because they are actually wrapped up with each other. The lumen, which is often denoted as (lm) is the standard unit of luminous flux. Sometimes lighting specifications list lumens rather than luminous flux, thus understandably leading some to believe that is a distinct measurement rather than simply an expression of a unit of measurement. Luminous flux simply refers to the total output of light of a light source.
Luminance is slightly more complicated and before going in to it is necessary to distinguish luminous flux from candlepower. Candlepower, which is now measured in candelas, refers to the intensity of light in one direction. Luminance is measured in candelas per square meter (cd/m^2) and refers to the luminous intensity of a point on a flat surface that is emitting light as perceived by the eye.
Well, that does it for now. I hope this article was illuminating and that the difference between lumens, luminous flux, and luminance is clear now. As usual do not forget to post any comments or questions on our blog or Facebook. Or, you can call us at 1-877-622-0897.
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