Need help using LM631 light meter

I thought it would be cool to buy a light meter to compare the various lights I will be aquiring. According to what I found on the CPF, the Meterman LM631 was the one to get - especially since they were offering a free digital multimeter in the deal.

It arrived today. The operating instructions were virtually nill. Regardless, I managed to turn it on to the "Lux" scale, and I experimented until I figured out how to set the "range". (At least I think I figured it out.)

It measured room light OK, but when I placed an ARC LSH-P in front of it, it went into "OL" (overload).

I called Circuit Specialists and talked to the techy. He said that I couldn't get that close with a flashlight. He gave me an RMA number to return it, but I don't want to return it if someone can explain to me how to use it.

Can anyone help?

Thanks,

Chuck /ubbthreads/images/graemlins/help.gif

Chuck, you'll have to press the far right button to get increases of multiples of 10, so your Lux number ceiling can increase... You're overloading your meter because when it comes on, it's in the 1-9.9 lux range only... You can increase it to 1,000+ with the "Range" button....

Pressing it once gets you to the 2 decimals range in lux, 3x gets you to 3 decimals, and 4x gets you to where you see the little "X10" light up near the bottom of the LCD screen... Now you're at 4 decimals range...

Something like a Space Needle II will require you to hit the "Range" button until you see the "X10" light up, and now, when you see "750", that means it's 750x10 or 7500 Lux, from 1 meter away...

And it must be measured at 1 meter away for Lux...

be sure to test the "peak" function once you get used to using it.. A lot of us have LM631's that have faulty peak functions.

In case you're not sure, the "peak" function holds the highest lux number attained until you re-set it, that way you don't have to try and remember the hightest lux number as you're moving the beam around on the sensor.

In this vein, how would you measure output in excess of the meter's capacity? I read in a post that at 2 feet you would Multiply (or Divide?) by a factor of 4 (in candle power). The 4x factor I understand, but forget which way it factors. The reason is at work we need to use a 1 million CP light for testing for leaks in a seal. They will want to know how we know it is 1 MCP. I can't flash them in the face like I would like to since "they" are customers, or more accurately, validation persons for my customer. This makes them somewhat illogical in all technical aspects and they must feel the need to quantify all aspects of every process to justify their existence. In my opinion. You and I both know that 700,000cp and 1,000,000 cp will show a leak equally well. The extra cp will not comprimise the seal unless it melts it. But we will need to measure.

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And it must be measured at 1 meter away for Lux...

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I had already figured out the range button, but like I said the instructions were minimal at best. They said nothing about how far the source should be from the light meter.

So, you are saying the test must be at 1 meter...hmmm. That probably explains the overload, because in the absence of adiquate instructions, I assumed I should put the light right on the meter. I tried measuring from a distance, but I reasoned that this could not be correct, because such a small percentage of the total light output was being "seen" by the meter. I'll have to give it another try.

Question: How are you guys interpreting these lux readings? I mean, how do you fairly compare two lights when they do not distribute their light in the same way?

Thanks for the help in understanding this,

Chuck

For measuring "Lux", you will need to make sure the distance from the flashlight to the light meter (or light recepticle) is 1 meter. Otherwise, the Lux readings will be off...

For the best comparison, you will want to move the flashlight (or the Meterman) around, so that the most intense part of the beam is shining on the little white light receptor on the meter. At one meter, the highest reading you get is the correct lux of that particular light...

You can also use the "peak" feature to force the light meter to keep, in display, the highest readings you will get from a flashlight's beam...

And another thing to consider is you'll want to subtract the light pollution, or the Lux that's already present on the Meterman before you shine a light on it, from the total Lux you have from a flashlight beam's lux reading, to get the correct number. For example, in a darkened room, you might still get 2 or 3 Lux. If a CMG Infinity Ultra gets 28 Lux, you'll need to subtract that 2 or 3 from it to get the correct reading...

Thank you for all your help, FalconFX.

I'll give it a try.

Chuck /ubbthreads/images/graemlins/smile.gif /ubbthreads/images/graemlins/smile.gif /ubbthreads/images/graemlins/smile.gif

NP!
/ubbthreads/images/graemlins/thumbsup.gif

FalconFX and Slick...

Well, just as you guys explained to me, holding the light at 1 meter makes all the difference in the world. And the "peak" feature seems to work fine.

So, now I will have to set up a stable, uniform way to measure my lights. Does anyone have a clever way to do that?

(It seems I always have one more question. /ubbthreads/images/graemlins/yellowlaugh.gif)

Thanks for the ideas!
Chuck

Chuck,
I usually find that a wall is the best way to get a clean, clear, and unobtrusive way to measure Lux with the Meterman and a light. Just use a meter stick or measure 1 meter from the ground (actually, from how far the light sensor is from the ground, as it's usually an inch or so from the ground) to the top and mark that length on the wall with tape or a tack or something identifying. Then, just place the Meterman on the ground and level the light with the tape/tack/ID length to 1 meter on the side of the wall, shine it down to the meter, and you get your reading...

You may have to place the Meterman and the light far enough from the wall to get a good hotspot to fall on the light sensor, but that's pretty much it.

Just one way to get an "apparatus" set up...
/ubbthreads/images/graemlins/grin.gif

Thanks again, FalconFX.

Chuck /ubbthreads/images/graemlins/smile.gif

I measure lux vertically.. - with the meter on the floor.

I also use the meter for "sorting operations" in a way that account more for total luminous flux, like a integrating sphere would do. To do this, you merely point the meter at the ceiling and use a power supply to light up luxeons sitting on an upside-down CPU heatsink. I also set a collimator on the emitter while doing this test.

The light reflected off the ceiling gives you a good indication of which are the best emitters.. I credit MrBulk as the source I first heard of doing this. Needless to say this is a very effective sorting technique.

Slick, you lost me.

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Slick said:

...total luminous flux ?
...integrating sphere ?
...collimator ?



[/ QUOTE ]

Chuck

Chuck,

Summation:

If you wanted to compare two lights, to see which light is brighter, you can have your Meterman set to a low lux demonimator (say 10-99 range), and then shine both lights, one at a time, at the ceiling, with your Meterman on the floor or table, or anywhere else.

The Lux number you would then get from light bouncing off the ceiling or surrounding room and into the Meterman will tell you how relatively bright one light is from another.

For example, say a 6D maglight has a very tight spot. If you shine its spot directly into a Meterman, your Lux measurements should be quite high. Conversely, if you have a Space Needle II, and shine it into a Meterman, the Lux reading should be quite high as well...

HOWEVER, shine the maglight into the ceiling and let it bounce off the walls and get a reading from the Meterman, and then do the same thing with a Space Needle II, and you'll be quite surprised that the Space Needle II outputs a lot more light.

This is not a measurement of LUX. This is a crude, albeit ingeniutive way of measuring total light output of two or more lights, in comparison to each other. You are, in essense, measuring how much light is being produced by the source by measuring how much "ambient" light it creates by bouncing off walls...

Flux is basically another way of saying total light output. An integrating sphere is used to measure total LUMENS from a source. It consists of putting the light source inside a huge ball (sphere), and measuring light output over 360 degrees (in all directions). Slick mentioned collimators because he was using it to place it on top of a bare LS, so that a focused beam of light can be directed at a wall, to compare relative brightness from one LS to another...

Hope that helps...

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FalconFX said:
Chuck,

Summation:

If you wanted to compare two lights, to see which light is brighter, you can have your Meterman set to a low lux demonimator (say 10-99 range), and then shine both lights, one at a time, at the ceiling, with your Meterman on the floor or table, or anywhere else.

The Lux number you would then get from light bouncing off the ceiling or surrounding room and into the Meterman will tell you how relatively bright one light is from another.

For example, say a 6D maglight has a very tight spot. If you shine its spot directly into a Meterman, your Lux measurements should be quite high. Conversely, if you have a Space Needle II, and shine it into a Meterman, the Lux reading should be quite high as well...

HOWEVER, shine the maglight into the ceiling and let it bounce off the walls and get a reading from the Meterman, and then do the same thing with a Space Needle II, and you'll be quite surprised that the Space Needle II outputs a lot more light.

This is not a measurement of LUX. This is a crude, albeit ingeniutive way of measure total light output of two or more lights, in comparison to each other. You are, in essense, measuring how much light is being produced by the source by measuring how much "ambient" light it creates by bouncing off walls...

Hope that helps...

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This is my standard method of measure light output. More times than not, I'm interested in total output. This method is the best way of providing that data. The bathroom works best, since it's usually a smaller room with good reflective properties.

What Choua & Nascar said.. /ubbthreads/images/graemlins/thumbsup.gif

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this_is_nascar said:
...This is my standard method of measure light output. More times than not, I'm interested in total output. This method is the best way of providing that data. The bathroom works best, since it's usually a smaller room with good reflective properties.


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That is what I did when I compared my SN II to nine incandescents. I was interested mainly in comparing total outputs relative to each other. Actual numbers were unimportant as long as the relationship was accurate. Here's an excerpt from that review:

...These tests aim to determine a light's total output by measuring INDIRECT brightness only... Please note that these tests are for comparative rankings only and are not definitive measurements of light energy...


INDOOR TEST #2 (METERED) "TOTAL LIGHT OUTPUT"

D3/P91: 27.9
Tigerlight: 26.9
Space N. II: 24.6
Ultra Stngr: 23.2
MagChrger: 22.7
D3/SRTH/N2: 22.2
Pelican M6: 19
TACM III: 18.3
PolyStinger: 18.2
Stinger HP: 18.2

...identical results for the PolyStinger and Stinger HP help to validate the testing procedure, since despite having different beams, the two lights have identical wattage and output.

I would like to have those relative figures verified by other Flashaholics.

Brightnorm