LUX vs lumens

We were trying to test some prototypes we had made on a lux digital light meter

It goes to 200,000 lux

and then after that just shows a 1, like an error I guess

Question is how does this convert to lumens?

I guess we need a much higher capacity meter for some of these leds lights huh

You don't need a meter with a higher ceiling, you need to move it back further.

And lux doesn't convert to lumens. They measure different aspects of light output.

what should the distance be?

didn't see too many lumen meters on the market, just lux

Lumens are measured with integrating spheres, which cost many thousands of dollars, but you can get good numbers with a homebuilt lightbox. (plenty of info on those in the search)

The distance should be a meter.

Lumens = radiant power output in all directions, weighted by eye sensitivity to wavelengths emitted
Lux = lumens / square meter

how an integrating sphere works is that it is basically a diffuse reflective sphere that actually captures ALL the light output in all directions, then diffuses it evenly. Designing one that is accurate irrespective of beam pattern and orientation of the light source is very expensive.

There is a method you can use to estimate lumens, which works if your light emits light in a circularly symmetrical pattern, and is sufficiently far away that it looks like a "point source":

Measure the lux output at a fixed distance of, with the light pointing directly at the target. Then point the light a few degrees off axis, and repeat. Keep doing this, and you will end up with an angular beam profile. You will then need to compute an integral to find the lumens.

Thread: 5mm LED Lumen Testing -- go here if you want more details.

You might try the Welcome Mat.

Wow what great feedback and info, really appreciate that guys!

Question: is a lux readout sufficient information for torch/flashl;ight gurus

meaning is getting ratings in lux ok and sufficient info?

What is considred a good lux reading at 1 meter?

For example on a 250 lumen bright LED, what might one expect roughly to see lux wise? or is that just too hard to say and does lux really not mean too much to you?

Lux is really a measure of how well a beam throws, and really doesn't tell you anything about how bright the flashlight really is.

A decent substitute would be a lux reading at 1m, in addition to listing the brand and bin of LED used, and what the drive current and voltage is. One could then estimate emitter lumens.

because lux is intensity at one point, it means a lot, but not the same thing as overall output, lumens. On these forums I always see lux measures at 1 meter.

like marduke said, lux measures how well a beam throws. So in a throwing light people will ask for as much as possible (some single LEDs can now break 30,000), while too much lux (too tight a beam) is actually inconvenient in a small EDC light, and not a good thing. But here are some general "good" numbers:

wide hotspot: 2-4 thousand
"tactical" light (med hotspot): 6-9 thousand
thrower: 20-30 thousand

and of course there are many lights inbetween.

http://flashlightreviews.com/features/lux.htm
http://flashlightreviews.com/features/lightbox_output.htm
http://flashlightreviews.com/features/output_vs_throw.htm#lumens