Just got my new LM631

[ZENGHOST]

Got my Meterman LM631 Digital Light Meter in the mail the other day (thanks for the link, Mr.Bulk) and thought I'd post some lux readings to see if they're comparable to the readings of others' lights (want to see if I'm doing this right). I figure the modded lights are going to put out different readings, but I list them anyway:

Mr.Bulk Space Needle II w/U5U: 6111
Pelican M6 w/W3V McModule: 1050
G2: 2760 (this one seems wrong--I kept getting different readings on it)
E2: 970
Mag 2D converted to 3 x 123 and Mag-num Star 6 cell lamp: 11080
L1 high beam: 254
L1 low beam: 4
Streamlight ProPoly 4AA 7LED 70
Micro-Illuminator: 66
Inova X5 (white): 62
Mr.Bulk LGI: 340

I'm hoping that someone else with an LM631 will have at least one of these lights so I can compare readings.

On another note--I was thinking about how the lux varies so much because of the size of the hotspot, etc. I was wondering if some sort of funnel could be used to funnel the light to create a hotspot that would be the same across all lights to try and measure total output. This way you would just shove the flash on the wide end and the beam would come out the narrow end. Would this work? Would the inside of the funnel need to be reflective somehow? I don't know too much about how light works, so I really have no clue if this would provide usable results.

 

[MR Bulk]

Hey ZenGhost, welcome to the world of flashlight reviewing, practically.

Couple of things:

1) shine from about a yard away (39.37 inches would be exact)

2) use the "lux" scale and turn on the "peak hold" function

This would be to measure hotspots. For general comparisons of lights especially with dissimilar beams, it is possible to get approximations by using the "integrating ceiling" method (bounce both lights off a matte white ceiling down onto your meter, sensor facing up), or try the TedBear suggested method -- shine both lights through the same beam diffuser (such as a translucent milk jug, etc.). You'd get comparative measurements at best, but at least they would put both lights on an approximately level playing field.

 

[PaulW]

ZenGhost,

You have yourself a good meter. I can give you only one comparison reading -- the LGI Classic. My LM631 measured 569 lux maximum with fresh alkaline batteries (at 1 meter).

Have fun with you new capability.

Paul

 

[ZENGHOST]

Thanks, guys. I'm not even close to "reviewer" level yet, but at least I can now offer more usable information on any lights that I post about. The free digital multi meter that came with it is also coming in really handy. Now, instead of guessing how much charge is left on my batts, I just connect them to the DMM to find out exactly how much.

The biggest problem I have right now is keeping an accurate distance (1 meter/39.37inches). I think I'm going to cut a string to length for that. I haven't tried the "diffuser" test, but will give that and the ceiling test a shot. I'm still curious about the funnel, though--I'll have to go find a funnel to try it with.

The other question I had was about the peak button--I can let my meter sit in a dark room until it zeroes out, but when I hit the peak button the stupid meter starts going up. What's up with that? I mean, how can pushing the button add light? No matter how long I let it sit at zero, the numbers start moving after hitting the peak button. A real pain. In any case, though, I'm pretty happy with my purchase.

 

[vcal]

Charlie.(or anybody else)....
Is the face of that meter illuminated in the dark?

 

[MR Bulk]

Meter is illuminated in the dark as long as you hold the "peak hold" button down for about two seconds.

Zen, the numbers will rise when you hit the peak hold, mine goes up to and then settles at 26; some people's (Slick is one that I recall) will settle on a different number, his is over a hundred, I think!

These meters are meant for OSHA guys in the field, to determine if the overhead lighting in an office meets minimum specs, etc., and thus the affordable price. Lab-grade meters are much more accurate but will probably cost in the several hundred- to several thousand-dollar range if absolute accuracy is a must. The LM631 gives us approximate measurements when compared meter to meter, and very close measurements when comparing two lights on the same meter. Error variance from reading to reading on the same meter can be 10%, and perhaps even more, which is why my published readings are usually an average of three readings for each light/application measured.

 

[Slick]

My meter would always go to ~117 (in complete darkness) regardless of range, so at 10x the error is HUGE! I talked to a tech at Meterman and found out that there was a range of serial numbers that are affected by this decfect. Since my meter is still under it's one yeard warranty (by just a few day!) they are going to exchange it for a brand new one. Metrers that are not under warranty get charged $68 - if memory serves me correct.

So I have been without my lightmeter for that past week and I can't believe how much I miss that thing.. /ubbthreads/images/graemlins/icon15.gif At least I'm getting meter that should have this problem resolved. /ubbthreads/images/graemlins/smile.gif