Lux and Lumens?

NightShift

Enlightened
Joined
Feb 4, 2001
Messages
380
Location
Long Island, NY
Im trying to familiarize myself with lux and lumens to determine if a figure is a lot of light, like when someone says 13,000 lux produced by a luxeon III - i have no idea what flashlight that could compare or come close to. Can someone put together a couple of popular flashlights and their typical lux reading (i.e. arc AAA, Arc LS, stock 3D m@g, 1w blaster, 5w blaster, surefire flashlight, x990 HID spotlight). And why is the X990 rated in lumens, not lux?
 

rlhess

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Apr 27, 2002
Messages
864
Location
Aurora, Ontario, Canada
Lux at one meter or, more properly, candela is the measure of the light in one direction in lumens per square meter. Total lumen output is the just that, the total output of the light. Some light manufacturers post the lumens of the finished assembly, measured in an integrating sphere while others advertise the total lumen output of the lamp, a significant percentage of which doesn't come out the front of the flashlight.

Go to http://www.flashlightreviews.com and while he doesn't measure lumens, he measures a propietary unit he calls "qups" and they are somewhat related to lumens, but done in a more home-brew analyzer.

His graphs of peak output (lux) vs total output (qups) are very interesting.

And yes, 13,000 candela is a heck of a lot of light from a flashlight. Oh and candlepower and candela mean the same thing -- but don't be misled with some claims.

There is a more detailed discussion of all this in the lighting handbook I have referenced on my Web site.

Cheers,

Richard
 

Quickbeam

Flashlight Enthusiast
Joined
Jun 19, 2001
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4,329
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FlashlightReviews.com
Lux is strongly affected by focusing optics and reflectors. Lumens is the overall output.

An analogy:

Imagine a water hose that, no matter how the nozzel is set, it always has the same volume of water out the end. A bucket would be filled just as fast if it was set to spray or stream. This is equivalent to Lumens. It measures overall output, or volume, of the water.

A water hose set to stream has all of the water focused to a tight point. A hose set to spray will cover a larger area with less pressure, even though the volume of water produced is the same. This is equivalent to how Lux is affected by focusing optics. A stream flow would have high Lux with all the water concentrated to one point, a spray flow would have low Lux with the water all going everywhere.

http://flashlightreviews.home.att.net/reviews/output_vs_throw.htm

As rlhess said, in my chart I don't measure Lumens, but I do measure "overall output" (volume) using a home-brew apparatus. I also measure Lux at beam center (focus) at one meter whch will give you an idea of how a light "throws". You can use this chart for relative comparisons between lights listed.
 
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