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Old 11-09-08, 01:40 PM   #18
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To measure lumens from a light source you typically use a photometer which counts photos. It has a defined size on the collector, you measure a precise distance from the source, and you need to know the directionality of the light (simply defined as the percentage of a sphere for elementary cases) to get your unit of lumens. So lumens has no accounting for the frequency of light.
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