A lot of questions keep coming up about the use of LUX in the reviews of lights on this site. Numerous times I have stated quite specifically that:

Lux is the measurement of the maximum output from the brightest part of the beam (the center). Lux is directly affected by focusing optics and reflector design.

Some manufacturers state the output of their lights or bulbs in Lumens.

Lumens is the measurement of the overall output. Lumens is all of the light measured no matter where it goes.

Many lights may produce the same number of Lumens, but different Lux at beam center due to the focus of the reflector.

Therefore, Lux is NOT a reliable measure of the overall light produced by a light. It only tells you how well the light is focused.

So, everyone asks, why don't you give both LUMENS (overall light produced) and LUX (light focused to the beam center)? Well, it's not that easy. Measuring LUX is easy, you just need a cheap Lux meter, which I have. To accurately measure LUMENS, you need an integrating sphere and all the associated equipment. If someone would care to donate the $10,000 - $20,000 for the sphere and the equipment, I would be happy to measure LUMENS for everyone. No takers? Didn't think so... (UPDATE: See LUMENS FROM LIGHTBOX READINGS???)

So, since my budget is a touch smaller than the $ figures stated above, I decided to put together this little apparatus to measure RELATIVE TOTAL OUTPUT from a light (NOT LUMENS!!!). The light measured would need to be reflected around and not from a beam directly striking the meter sensor. It had to be something similar to shining the light at the ceiling of a white room and having the meter on the floor, thereby getting a sense of the overall reflected light that hits the sensor. Since I don't have a spare room painted white on all six sides, I needed a box that was white on the inside. How about a milk carton? White, cheap, easy to replace, and easy for almost anyone to replicate!

I covered the milk carton with aluminum foil to avoid light leakage in or out. 2 holes were cut - one in the center of the side for shining the flashlight through, one on the bottom for the meter sensor. A 1" x 3" strip of paper was taped to the inside of the hole on the side to act as a baffle so that none of the beam from the flashlight would directly strike the meter sensor.

[UPDATE: I removed the "bottom" (side opposite the illumination port) and the entire inside of the box was coated with 2 coats of Red Devil Acrylic Latex Enamel RDHP2402 Satin White paint. Result: Almost identical readings. So it appears that "whiteness" of the box is not really a factor...]

Ta-Da! A light meter and a milk carton!

A bunch of people have been asking what the baffle looks like so they can make their own lightbox. Here it is. This piece of paper hangs down about 1/2 inch inside the 180 deg. arc of the top hole nearest the light sensor.

The methodology was very simple - hold the light in the center of the top hole, bezel even with the surface of the carton, shine the light straight down and take a reading. Is this super scientific? Absolutely not! Is is comparing the relative amount of overall reflected light from the flashlights? Pretty much, yes!

So, we may not have an integration sphere, but at least this should give a general idea as to which lights' output are brighter overall than others. The brighter the light, the more reflected light that will hit the meter sensor. Also, lights with the same battery/bulb configuration should read the same regardless of how tight the beam can be focused with the reflector or optics.

With this apparatus, for example, a single white LED 6V light that is focused to a tight beam should read just about the same as a single white LED 6V light that has no optics and just produces a flood of light.

NOW REMEMBER - there is a lot of room for error here, so I wouldn't say specifically that a light with a reading of 500 is necessarily putting out less light than a light with a reading of 510. Suffice to sat that these 2 lights would be just about the same. However if you see a reading of 500 vs 2000, it should be safe to say that the 2000 light is about 4 times brighter than the 500 light. I'd say at a guess that if the numbers are within about 15% of each other, they're putting out about the same amount of light overall.

Incidentally, I have had one person who uses a similar but different method of overall light measurement report that the numbers they have obtained correlate with mine! That means that the data from this project is somewhat valid!

UPDATE: The data has been combined in a chart with the LUX readings of many of the lights so you can see "throw" and "overall output" in one chart.

By the way, we had an official naming contest for the units produced by this device on CandlePowerForums some time ago and the winner was QUPS (Quickbeam's Unofficial Photonic Standard) - Just in case you see the overall output numbers mentioned as QUPS on CPF (my username on CandlePowerForums is Quickbeam...)