What do i need to measure the brightness of my flashlights?

[fstuff]

i keep reading people saying this light has a xx Lux at 1m, and throw at a range of xxx feet.

How do they do that?

And how can I do that w/my lights?

 

[Marduke]

They use a light meter. Lux at 1 meter is a useful measure for lights meant to be throw monsters, but it doesn't really tell you how bright a light actually is, just how intense the hotspot is.


The total distance a light is capable of illuminating is just based off objective observation.

 

[lronchef]

So is there a somewhat inexpensive, good "bang for the buck" light meter out there recommended for the average light nerd to measure the various outputs of his many torches?

I recall my mother using a light meter to measure flash brightness. Same thing?

I seem to recall a formula from "flashlightreviews.com" indicating what lumen ratings were from reading lux? Anyone here have some type of formula for determining lumens at varied distances?

 

[Marduke]

You cannot convert lux to lumens because the beam pattern is not constant and varies W.R.T. the angle away from centerline. The formula on FLR was to do a rough conversion from his "total output" measurements from a lightbox into lumens.

 

[Bullzeyebill]

You can use a light meter to compare the output of various light you may have. At some point you can sort of figure some approximate lumen ratings. Bounce with a lightmeter is what I use, and many CPF people use. Some (hi Marduke) will say that the different beams will produce different lightmeter readings bouncing off of a ceiling, but overall, you can get some good approximate output ideas.

Bill

 

[Yoda4561]

The proper tool for measuring total light output is an integrating sphere, and those will run many thousands of dollars. Everyone who doesn't work at a place that has an IS uses a relatively inexpensive light meter(you can find these under 100 bucks), often in conjuction with a home-brew integrating sphere made of white styrofoam or similar. Homebrew integrating spheres aren't anywhere near accurate, but by comparing lights you own that have reliable lumen figures you can compare them to your numbers and get a "correction factor" of sorts. With some trial and error it's possible to get fairly accurate numbers.

If it's just the brightness of the light you want to measure, like how intense the hotspot is compared to the spill all you need is the light meter and a standard distance to use for comparison.

 

[MWClint]

You can use a light meter to compare the output of various light you may have. At some point you can sort of figure some approximate lumen ratings. Bounce with a lightmeter is what I use, and many CPF people use. Some (hi Marduke) will say that the different beams will produce different lightmeter readings bouncing off of a ceiling, but overall, you can get some good approximate output ideas.

Bill

couldnt you consider ceiling bounce in a bare room with white walls and a light colored carpet, pretty much a large scale integrating sphere?

 

[Bullzeyebill]

couldnt you consider ceiling bounce in a bare room with white walls and a light colored carpet, pretty much a large scale integrating sphere?

You can experiment with your enviornment. I use a small bathroom with no outside window. Whatever the enviornment, keep it the same, and if you do change it, do a baseline with one of your lights that has consistant output so you can adjust your lightmeter lux, or fc numbers.

Bill

 

[fstuff]

$30 Lightmeter at DX:
http://www.dealextreme.com/details.dx/sku.7954

How is this for what i need? any alternatives?

 

[Illum]

as far as equipment goes...first your going to need a ball
http://www.candlepowerforums.com/vb/showthread.php?t=200334

a light meter can measure lux output in the hotspot, but tells you nothing about the total output [lumens] of your light

 

[Bullzeyebill]

as far as equipment goes...first your going to need a ball
http://www.candlepowerforums.com/vb/showthread.php?t=200334

a light meter can measure lux output in the hotspot, but tells you nothing about the total output [lumens] of your light

A llight meter used with a self made light box, or IS can give you much information about the output of your light particularly when compared to other lights that you may have access to. You can, in a roundabout way, get some approximate lumen numbers. You can also get some results about total output of your light using simple bounce with a light meter in a controlled enviornment, again comparing out with other lights. We are not talking rocket science, and approximations only, but why not take advantage of what we can easily use. A light meter does not cost much, and does not have to have the accuracy of scientific equipment to be a useful tool for flashaholics. How many times have I said this here in CPF. Good tools for flashaholics are a DMM and an inexpensive light meter. If we do not use such easily obtainable tools, we will only be putting out or relying on received subjective information about lux, and light output, current draw of various lights, and voltage info that we need to know when dealing with Li-Ion cells, and on and on. Let us leave subjective conversation to such issues as tint, LED vs Incan, individual preferences to one light over another, etc.

Bill

 

[precisionworks]

Illum_the_nation said it best ... first you're going to need a ball.

The IS is not hard nor expensive to build, and it provides the most useful information. Lots of members use the Meterman LM631, around $100 online. I bought the Extech EA31 because a seller had it listed at $80. Figure another $50 for materials to build the Integrating Sphere & you are ready to go.

Good tools for flashaholics are a DMM

+1

Whenever possible, I measure amp draw at the same time as measuring light output. It's interesting to watch how some lights keep the amp draw very stable, where others vary widely.