LUMEN METER OR BOX

No idea if this is the correct area as I have an odd question.


I have heard 20x now that DX has a "lumenmeter" or "lumen box" is this true..or part true?

Any reviews or info on this?

Yes, they do have a Lux meter.

Hmmm interesting, does anyone know how to convert from lux to lumens or have a just made a twot of myself for asking that.......

Welcome Mat to the rescue!

Q: What's the difference between "lumens" and "lux"?
A: Lumens measure the total amount of light output from a particular source. Lux measures the intensity of the light hitting a specified area. For example, an ordinary household lightbulb generates about 1000 lumens, but the intensity of its light at a particular point, such as on a book you're reading, will be comfortably low. Almost all flashlights rely on an optical device such as a reflector or lens to squeeze most of their output into a small area, which allows you to illuminate a point of interest with enough intensity, but without requiring a lot of power. To illustrate this concept, try the following: First, look at your room's ceiling light. In all likelihood, you can stare at it without much discomfort. Now, try looking into a weak flashlight like a traditional incandescent Mini-Maglite. You'll notice that it seems very bright. This is lux. Now, remove your Minimag's head to put it into candle mode. Try switching between its output and your ceiling light's output. Since they're now illuminating approximately the same area, the much higher lumen value of the ceiling light will provide much higher lux values at a chosen point. An extreme example of high lux and low lumens is a laser, which doesn't really create that much light, but focuses it into a tiny, brilliant point.

Lumalee said:

Hmmm interesting, does anyone know how to convert from lux to lumens or have a just made a twot of myself for asking that.......

Click to expand...

Tigerhawk already said it.. So a little different approach:



Converting lux to lumens can only be done if the lightsource is fully omnidirctional (without reflector).

Lets assume a particular light puts out 20 lux at 1 meter omnidirectional (20 MSCP.): The conversion to lumens: lux* (4*pi)= 251.4 lumens..

Now if you concentrate most of those lumens into a narrow beam (reflector), the amount of lumens (theoretically..) stayes the same. However the lux-reading within the beam is much, much higher than the bare source. This is caused by the fact that the light is no longer omnidirectional. So here lux cannot be converted to lumens.

I someone points a flashlight at you from a distance, hurting your eyes, two conclusions are possible: That someone has a huge omnidirectional lightbulb in his hand. Or he just has a flashlight.
As long as you are at the center of his beam, you cannot tell which of the above is true! Ofcource, common sence will tell it's a flashlight.

If I point Maxablaster at you from a distance of 10miles (with 55,000,000 beam-cp) it will have the same effect at you as if I had a bare lightbulb producing 691,350,000 lumens, which is virtually impossible !! This to illustrate the power of a (high quality-) reflector!

The amount of light produced by a flashlight (torchlumens) can only be measured with a integrating sphere, thats a kind of lightbox- or ceilingbounce-test.

Measuring the lux-output of a flashlight at a certain distance, only gives you more information about the throw of the light (beam-cp)

Indeed a laser has relatively low lumens-output, but cp-rating (lux at 1 meter) within the beam is very high!



Regards,

Ra.

TNX TigerhawkT3 a fantastic way of explaining the scenario to a newcomer, and Ra as ever your scientific approach interests me more than anything, in fact anything that mentions the maxablaster interests me. To help you somewhat, I am looking to do comparison test between various lights in a simple control environment, and it seems the majority of people are happy with lumens figures as it is what a lot of the sales jargon uses and thus gives a very simple datum to work with that is fairly universally understood, for example in comparing light A output against light B output and also to see how close anufacturers claims are.
No intentional hi-jack of thread will start another if requested, but gratefull for the thread "heads up"

Lee