I am perusing DealExtreme to make a few purchases based off recommendations here in the LED section. I like the idea of sub-$20 lights that perform very well. But when looking at the specs of them, alot of them don't give a lumens rating it gives "- Light meter test: 1000 lux @ 1M" that instead. What is it and how does it relate to Lumen output?
First, a lumen "specification" means nothing, since it's subject to the imagination and creativity of the marketing department. And they get creative indeed. It's possible, however, that the lux value was actually measured, so there's a better chance that it means something.
There's no fixed relationship between lumens and lux. Lumens represents the total light output from a light, all together, in all directions. Lux is the brightness in one particular direction and distance from the source. So a 100 watt light bulb, for instance, might put out a lot of lumens, but it'll have a relatively small lux value in any direction since those lumens are spread around all directions. But if you put a reflector on it making a 100 watt spot light, the lux value (in the direction of the main beam) will be much greater even though the total number of lumens will be essentially the same, because you've concentrated the lumens into a beam. The lux values in directions outside the main beam will be less than for a plain bulb, of course. But a single quoted lux value almost always means lux in the direction that the light is brightest.
The square root of the lux at one meter tells you the "throw", or the distance at which the light will illuminate an object with a brightness of 1 lux(*). For example, if a light's main beam produces 100 lux at one meter, it'll light up an object 10 meters away with a brightness (technically, illuminance) of one lux. You need to increase the lux at one meter by a factor of four to double the "throw".
(*)Once again, marketeers are creative and sometimes define "throw" at a lower illumination level. For example, a light having a main beam intensity of 100 lux at one meter might be advertised to have a "throw", "effective distance", or some such of 20 meters rather than 10. If you look at the fine print -- if there even is any -- you'll see they're defining "throw" as the distance at which you get an illumination of 1/4 lux.
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