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Tuesday, March 17, 2009

What’s a Lumen? - from Light and Motion's website

Short answer, a lumen is the unit measure of the luminous intensity of a light source. The more lumens, the brighter the light.
You want the long answer? Okay, here you go: Luminous flux is the measure of the perceived power of light. A lumen is the SI unit of luminous flux. One lumen is defined as the amount of light produced by a light source that emits one candela of luminous intensity over a specified angle.

Previously, many light manufacturers listed "output" in watts, which is incorrect. The Watt is a measurement of power consumption, not light output. For example, a 1-Watt LED can produce 120 lumens of light because of the inherent efficiency of LED's. To get the same output from an incandescent bulb (like the ones that you use in your lamps at home), you'd need to use a 4-Watt bulb. So 1 Watt for LED's versus 4 Watts for Halogen—but still the same 120 lumens of output. You can see how people were confused. We list our power in lumens to give you the clearest "apples-to-apples" comparison possible.
The best LEDs can produce 120 lumens at 350mA, or about 1W. Halogen bulbs (optimistically) produce about 30 lumens per Watt. This means that a Halogen bulb would require 4 Watts to produce 120 lumens, consuming 4 times the battery power of the LED!

Thanks light and motion....


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