ShopHDE has the Professional Digital Light Meter for $21 - $5 off with coupon code benjulydb456f [100 uses] = $16 with free shipping. Measures up to 50,000 lux with ±5% accuracy. Shipping is from U.S. and is free for all orders.
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I have several flashlights. One of them is rated 800 lumens, and one of them is rated 630 lumens. The other ones are rated at different power levels. I was wondering if something like this could test to see if they are anywhere close to rated lumens. Is there a conversion from foot candles/lux to lumens?
Mmm, I don't know the accuracy of Google results sometimes lol, but if you do a search for lux to lumens there are a few sites offering converions... and a few people go into more detail in a few forums about what to do to figure it out.
I think I misread your question a little haha. So.. this is what I found, let's see if it helps any... this tool would rate the lux, and the fundamental ratio of conversion from desired lux level to required lumens is: 1 lux = 0.0929 lumens per square foot. But there are other factors that go into everything like the radiance properties of the light (candle versus a narrow beam from a flashlight).
Not really, this would measure illumination over the sensor surface and so while you could shine a flashlight at it, you'd be trying to exactly match the size of the hotspot from the light but then wouldn't be able to measure any of the spill which is usually a fair % of the total output.
IF it has a focusing lens instead of just a reflector it could come closer to having a sharp cutoff from the hotspot and minimal spill loss but the lens itself would be reducing total output instead.
If they are generic branded lights, you're probably getting somewhere between 50 to 70% of the light they're rated for. If major brand lights, you can probably find someone online that has tested it and has the data on how it performs.
Another option is that by considering what LED type and bin it uses, you can measure drive current to the LED and then consult the LED manufacturer's datasheet for lumens @ drive current used, then depending on lens and/or reflector type, subtract an appropriate % for losses from those... then if you want to get even closer to accurate, measure LED die temperature and consult the spec sheet for the derating @ running temperature too.
I went ahead and ordered one, just to play with. Another gadget.