Lux Meter Questions

[WadeF]

I got the $28 LUX meter from DX. It seems to be reading very low. Comparing results from some of my lights to results done by other review sites, etc, I seem to have to add 50% to the results it gives me to match their results. Is this something I can do consitently? So if I get a reading of 3,000LUX, or 20,000LUX, can I simply add 50% to get a more accurate figure, or does that not work out? I know with light there are all kind of curves and what not involved, so I don't know if I can just add 50% to any reading.

My Sekonic 408 light meter would give me EV values that would translate (via Sekonic's EV to LUX chart) into numbers that were right on with the #'s the review sites were posting, but the chart only gives a conversion for every 0.5 EV which could be 10,000LUX to 15,000LUX leaving me to estimate inbetween.

 

[Glow_Worm]

Re: DX LUX Meter questions.

Wade,

I have the same meter, and in my case the readings I get seem to be as much as 2X lower than others report for the same light. However, it seems to be pretty consistent in readings, so it is still useful for comparing relative brightness between lights on the same meter. But definitely not for comparisons w/ other folks (even for those who have the same meter apparently).

I had a friend try to translate the Chinese instructions, hoping that there might be some magic combination of holding certain buttons while powering on to trigger a recalibration or some-such, but she said there didn't appear to be any info like that contained therein.

Seems to be a case of you-get-what-you-paid-for here. Good for comparisons on the same meter, but definitely not accurately calibrated.

--kirk

 

[Norm]

Re: DX LUX Meter questions.

There may be calibration pots for each scale internally but without a calibration standard you'd be flying blind.
Norm

 

[VidPro]

Re: DX LUX Meter questions.

it works great , reviewers get special lights that work 50% better than the production lights they sell us peasants
they also get special nuclear added batteries that last hours longer, but thats ok cause reviewers have to have flame resistance anyway

 

[adirondackdestroyer]

Re: DX LUX Meter questions.

I ordered this very same Lux meter and it arrived today. I feel like a complete idiot saying this but I really don't completely know how to use it. Should I always have it on the 200,000 rating? I should be taking readings from 3 feet away, right?

If someone could give me a few basics on how to use it that would be great.

Thanks

 

[thekobk]

Re: DX LUX Meter questions.

I was thinking of getting one of these my self. How much do lux meters cost from other places?

 

[Glow_Worm]

Re: DX LUX Meter questions.

I attached mine to a tripod using the mounting hole on the sensor, and set the tripod height to be the same as a nearby table. I then measured 39.4 in. (1 meter) to the table & marked the spot on the table w/ a bit of tape. I place the flashlight on the mark on the table, usually with the lens at the mark (I don't know if you should measure based on the lens or the LED itself; prob. the LED would be better, but that's more difficult to judge).

Then I shine the light on the sensor, and move the hotspot around on the white dome until I get the highest reading. I use whatever scale is most appropriate for the light. For a light <2000 lux, use the 2,000 scale, for most of my brighter lights I use the 20,000 scale. Only my very brightest lights (Mag85, Aspheric Mag) need the 200,000 scale.

If the light is too bright (over 2000) for the chosen scale, the meter just displays a 1, so then I switch to the next higher scale. You could use the 200,000 scale for everything, but then you won't get as exact a reading, i.e., you'll lose the last one or two significant digits. For example, you get 1996 on the 2000 scale, vs. 199 (x10) on the 20000 scale, vs. 20 (x100) on the 200,000 scale.

Hope that makes sense. And oh, the Hold button is essentially useless.

--kirk

 

[TorchBoy]

Re: DX LUX Meter questions.

Glow_Worm, what's the brightest reading you've made with it? Direct sunlight perhaps?

 

[Glow_Worm]

Re: DX LUX Meter questions.

TorchBoy,

Yes, direct sunlight. About 61,000 outside today on a sunny afternoon. Maybe closer to 100K at noon-time in the summer I'd guess. Though I can hit 150K if I hold the D-Mini right on top of the sensor.

--kirk

 

[WadeF]

Re: DX LUX Meter questions.

Does anyone know the proper way to take LUX readings at 1 meter? Do you measure 1 meter from the lens, or 1 meter from the emitter / bulb?

Also does anyone have a high accuracy meter that is known to be accurately calibrated? If so maybe they could share some 1 meter readings from some popular lights, like a Fenix P1D-CE, Surefire E2e, G2, etc, so we can see how our meters compare.

 

[TorchBoy]

Re: DX LUX Meter questions.

Do you measure 1 meter from the lens, or 1 meter from the emitter / bulb?

If you're measuring torch lumens (which you can't help but do) then it should be 1m from the lens.

 

[Codeman]

Re: DX LUX Meter questions.

Does anyone know the proper way to take LUX readings at 1 meter? Do you measure 1 meter from the lens, or 1 meter from the emitter / bulb?

Also does anyone have a high accuracy meter that is known to be accurately calibrated? If so maybe they could share some 1 meter readings from some popular lights, like a Fenix P1D-CE, Surefire E2e, G2, etc, so we can see how our meters compare.

An excellent place to start would be Light Meter Benchmark Testing – CPF style.

 

[emitter]

Re: DX LUX Meter questions.

mine reads low as well, compared to a calibrated Extech meter at work. I tried futzing with one of the trim pots on the main board, and did tweak it closer to the Extech, but the response still isn't the same. I use it for what it is, especially for room lighting. Supposedly it was calibrated to incan spectrum, I read someplace. Most importantly, it is built just as well as all the others and has a usefull range.
I just bought the DX ir thermometer gun too.

 

[thekobk]

Emitter could you post some readings of your meeter testing common house hold light so we have some sort of baseline to calibrate ours to? Like a 60watt and or 100watt house bulb.

 

[LuxLuthor]

You guys need to understand the wild variations in comparing meters. The distance from a 60-100W bulb, type of bulb, age of bulb, angle of sensor, background light, temp, etc etc all affects readings.

Probably the most useful thing is to use the same one to compare one light source against another. That's what I have been doing with incan bulbs here.