5 luxmeters compared (april 2018)

Thanks for the test djozz!
I’m glad that I waited for it.

Thanks.

I wonder if some uncertainty could stem from measuring the lux from a slightly different spot in the beam? Did you happen to do some spot checks in a sphere which would probably result in more consistent readings?

I see an extreme inconsistency now, according to the wavelength response, the UNI-T meter should read nothing for the 400 nm led, but instead gives the highest reading of them all. Will check tonight if that reading was correct.

I tried to find the highest reading in the spot every time. My findings are that if the output of the flashlight is constant, measuring like this is pretty consistent. I did not do it this time but in another occasion comparing luxmeters, for each flashlight, after measuring with the last luxmeter I did a second reading with the first luxmeter and got virtually the same result.

Yeah, I guess at 7 meters the spot is quite big which makes it a bit easier.

LOL, here is part of the solution, the five detectors illuminated with 400nm light: two of the 5 diffusers actually show bright blue fluorescence!! :party:
(if I were to design a luxmeter :nerd_face: …well, never mind)
Luckily the common white leds we use do not emit close to 400nm!

Btw I didnt double check the pic. But mine isnt the same to the one I just mentioned. Name looks similar though. In your results the LX1010b has in 3 out of 4 (excluding the UV) tests the lowest numbers.

Funny how similar this is to Sound pressure meters and respective frequencies. I have been in audio for decades and this discussion is almost word for word the same.
The difference being sound meters all come with the response curves and different weighting for relevance in different environments. The color spectrum might be a little more complicated.

Thnx Djozz. Its bin a while since I did cd measurements. But I believe I am doing something wrong. I use the rapid tables converter for lux to cd. But for instance when I fill in the ± 1400lux of your Mitko thrower at 7m, I get 69 kcd, wich should be much higher.

Probably having a brainfart, can someone help me out. :weary:

No, nothing wrong with your calculations, none of the flashlights that I used for these tests were at maximum modes, but on a well regulated lower mode to obtain a flat output.

Thnx! Guess my mind can only think in max lumens and max kcd. Thanks again for the test. I only have the uni-t, but I also find it to measure 10%+ to low.

Thanks djozz :beer:

Thanks djozz. I wont mention invaluable but will say useful information. :stuck_out_tongue:
What would a rough price on each meter be?

You’re welcome. It isn’t invaluable to me either, I just find this measuring stuff lots of fun, especially when antique optical instruments can be used :slight_smile:

The newprices for the meters at the time I bought them were:

MobiLux Class A : 1400 dollar (but bought 2nd hand)
Tasi 632A: 135 dollar
LX-1330B: 27 dollar
Tondaj LX-1010B: 22 dollar
Uni-T UT383: 12 dollar

.
It is good to hear that my struggles are not unique :slight_smile:

Yes, there are complications in light measuring that are probably not present in measuring sound (but I have never been into measuring sound, it will for sure have its own pecularities). So much that an overall measurement error of 10% is already considered very good. What does not help is that even the most expensive luxmeters do not come with detailed wavelength/response data, if you are lucky you get a maximum overall error for that and that’s it.

And with the way we use luxmeters we do not even have to deal with how different luxmeters respond different to the incoming angle of the light, because with throw measurements the angle is always close to zero.

Great tests Djozz! I’m glad I found that TASI632. Now I’m more confident with all my measurements. This is a lux meter with decent accuracy across the full visible spectrum without breaking the bank.
I played with a DIY crude goniometer using my TASI632 but I’ll need to make new slit hole to it. 1mm seems to large for close range input.

- Clemence

What I did find out with the Tasi meter is if you measure at the very low end, under 10 lux, the reading gets inaccurate by static charge or capacitance or whatever something on the cable between meter and sensor, it can give an off-set error as large as 1.5 lux. If part the cable is resting on a metal surface (in my case the chunky monochromator) that error is gone.

Correct!
Never measure anything under 1 lux near metal objects and electronic devices placed close to the cable. When the USB connected, it will also adds ~1 lux to the measurements. And try not to move the cable after zeroing. It’s not EMI shielded.

- Clemence

Thanks for this test Djozz !

Since i want a lux meter to test modded lights , which includes lights with dedomed emitters , should i get the Tasi 632A ? Thank you

You did notice correctly that cheap meters especially struggle with measuring dedomed emitter spectra correctly.
But it depends entirely on how nerdish you are on the numbers, are you prepared to spend 5 times more money to gain a couple of percents more accuracy?