Electronics, Lighting, & Gadgets - Lux...lumens...? Which is the right way to measure output?

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Kabir424
12-14-08, 10:09 PM
AYUP- LCP4N
Light Unit Output - Upto 7500 - 8000 lux @ 1 metre, approx 320 lumen

http://www.ayup.com.au/specs.php#CREE%20LIGHTSETS

The LUMOTEC IQ Fly with a sensational illumination output of 40 lux.

http://www.sjscycles.co.uk/product.asp?pf_id=15238&src=froogleUS&currency=USD

Fenix LD20 Q5
Turbo Mode: 180 lumens

https://www.fenix-store.com/product_info.php?cPath=22_65&products_id=362



So, how is it that the first light has between 7,500 and 8,000 lux(about 320 lumen) and yet the IQ Fly only has 40 lux? Apparently the IQ Fly is significantly brighter than a Fenix LD20 Q5 which has 180 lumens. So IQ Fly should probably be comparable to the first light in lumens but the lux is off by a rediculously large margin. And, what is the appropriate way to measure output for lights? Why don't they all just give one measurement?

bikinfool
12-14-08, 10:27 PM
It would be nice if there were some standardized measurements...but the whole story isn't told by either lux or lumen measurement either. Reminds me of trying to choose an audio amplifier based on advertised output wattage...
Shimagnolo
12-14-08, 10:39 PM
The big variable is focus.
Lumens tells you how much light is being produced.
Lux tells you how much light is hitting a square meter of surface.
Think about the difference between the light radiated by a bare bulb, versus the same bulb with a big sharply focused reflector behind it.

znomit
12-14-08, 11:06 PM
Yeah the AYUPs are lux at 1m.
Light spreads out with distance so using the inverse sq law at 14m it will be 14^2 times less. 41lux. So kinda similar to the fly.
These are very rough calcs.

Lux is a better measurement for the user because its actually what you see, along with a beam pattern. Lumens are better for the manufacturer because they just quote the Cree/SSC datasheet.