Using a Lux Meter without a light box

After seeing a couple threads here about creative members that have built these spherical (sp?) light measuring boxes I decided to purchase a Lux Meter to play with. I bought the $40 one off one of the Amazon vendor so I'm not expecting lab environment accuracy.

I don't really have a good place to store such a light box so i was wondering how accurate a comparison between torch A and torch B would be if I just use the old ceiling bounce test.

The setup:

A room as near to pitch black as practical
Read the lux meter for a zeroing read
Place lux meter off center in the room
Place Torch A in the middle of the room on a fixed height table
Torch A pointing up in candle mode.
Turn on Torch A and read Lux meter reading and record 3 average reads
Repeat with Torch B
The torch with the highest number is brighter?

Sounds simple but I'm a newb and not sure if/how a floody reflector and a throw optimized refelctor on different lights would skew that number.

Thoughts, comments?

Thanks as always for the education.

Bob

It should work to give you an idea of how your particular lights stack up against eash other. It's fairly easy to configure a "box" of some sort to collect the light, then just cut a spot for the sensor in one of the sides.

It won't be perfect either, but should work better than a ceiling bounce.

You should ask Selfbuilt about this, since he does both lightbox and ceiling bounce measurements when testing a light. He says the ceiling bounce method is more accurate, since it's less prone to be thrown off by the beam profile.

I regularly use the ceiling bounce test to compare the percentual difference of brightness between flashlights. Then I shine the lights above the sensor. The important thing is to take in consider the beam size diameters and hold a light with wider beam closer to the ceiling so the projected beam will be equal with every light, OR measure the highest possible value.
This method makes the demand of a beam with a limited profile, some multi-LED lights without reflector will not work, because the light will be spread to the sides and shine up the wall.

Regards, Patric

Inspite of not having a lab to do the tests youre differences would be 100% accurate from light A to light B if all the variables are done the same way.

It is like using a scale that says I weight 5lbs extra. If on the same scale I lost or gained 10lbs the increase or decrease would be accurate because I am using the same scale with the same variables.




Variables could be:

• fully charged cell at 4.1v
• in the man room at 7pm with curtains closed
• ect....

IMHO I say the lux differences withing your lights would be accurate if you keep the variables and use the same lux measuring tool. If you compared your Lux tool vs. someones elses Lux reading tool then the accuracy would suffer, but a general idea of output will still be interpreted.

Thanks for everyone's insight. Since posting and playing with the ceiling bounce I have built a very simple light box but it was a total bomb as I was getting lux reading on a 6P with an M60 around 140 LUX. My calculations would put that closer to 5000 lux if you use the rough lux x 25 equals roungh lumens. oh well more studying in that area needed. Until then the ceiling bounce testing is fun.

Bob