Light Output Measurements: Difference between revisions
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'''Emitter lumens''' LED manufacturers publish specifications listing the lumen output of their LED's (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. | '''Emitter lumens''' LED manufacturers publish specifications listing the lumen output of their LED's (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 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. | ||
However, a flashlight rarely has consistent output. Instead the output usually drops off early as the LED heats up. So the initial output can be fairly high and then drop by 10-20% within a few minutes. Depending on how well regulated the light is, the output can continue to vary with battery voltage. | However, a flashlight rarely has consistent output. Instead the output usually drops off early as the LED heats up. So the initial output can be fairly high and then drop by 10-20% within a few minutes. Depending on how well regulated the light is, the output can continue to vary with battery voltage. | ||