Light Output Measurements: Difference between revisions
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Lumens are a measure of the total light emitted by a LED or flashlight (see [http://en.wikipedia.org/wiki/Lumen_%28unit%29 Wikipedia article] for more information on lumens). For scale, a 60-watt incandescent lightbulb produces 890 lumens, a 40-watt bulb is 460 lumens, and a pretty decent flashlight produces about 200 lumens. Lumens are sometimes measured "at the emitter" or "out the front." Emitter lumens will always be higher than out the front lumens because there are some losses involved as the light bounces off the reflector and is filtered somewhat by the flashlight lens. | Lumens are a measure of the total light emitted by a LED or flashlight (see [http://en.wikipedia.org/wiki/Lumen_%28unit%29 Wikipedia article] for more information on lumens). For scale, a 60-watt incandescent lightbulb produces 890 lumens, a 40-watt bulb is 460 lumens, and a pretty decent flashlight produces about 200 lumens. Lumens are sometimes measured "at the emitter" or "out the front." Emitter lumens will always be higher than out the front lumens because there are some losses involved as the light bounces off the reflector and is filtered somewhat by the flashlight lens. | ||
'''Emitter lumens''' LED manufacturers publish specifications listing the lumen output of their | '''Emitter lumens''' LED manufacturers publish specifications listing the lumen output of their LEDs (see [[Brightness Bins]]) and sometimes flashlight manufacturers will just take the highest value for the LED in their flashlight and say that is the output. But actual output depends on the voltage and current delivered to the LED. Even then, these numbers are always going to be higher than the actual light output by the flashlight. | ||
'''Out the front lumens''' To measure the actual light output of a flashlight, an integrating sphere (see [http://en.wikipedia.org/wiki/Integrating_sphere Wikipedia article]) is needed that captures all of the light and distributes the light equally so that it can be measured accurately regardless of whether the flashlight has a small hotspot or a wide flood. [[Terminology#CPF|CPF]] users MrGman and bigchelis have calibrated integrating spheres, test flashlights that people send to them, and publish their results in posts that are stickied in the [http://www.candlepowerforums.com/vb/forumdisplay.php?f=45 CPF LED Flashlights] forum. This way different flashlights can be compared using consistent test procedures. | '''Out the front lumens''' To measure the actual light output of a flashlight, an integrating sphere (see [http://en.wikipedia.org/wiki/Integrating_sphere Wikipedia article]) is needed that captures all of the light and distributes the light equally so that it can be measured accurately regardless of whether the flashlight has a small hotspot or a wide flood. [[Terminology#CPF|CPF]] users MrGman and bigchelis have calibrated integrating spheres, test flashlights that people send to them, and publish their results in posts that are stickied in the [http://www.candlepowerforums.com/vb/forumdisplay.php?f=45 CPF LED Flashlights] forum. This way different flashlights can be compared using consistent test procedures. | ||