lux meter android app results

Seattle Sparky · Jun 13, 2015

Here are the max results I have got using Light O meter app on my android with some of my lights.

All measurements are taken at 3 ft. Using Galaxy s4.

HDS :
170N clicky--------------4759 lux
200N rotary--------------4,905 lux
Hyper Red clicky--------10,520 lux
200 clicky w/ xpg2 5k---8,387 lux

Surefire e1d---------------9,985 lux

Zebralight:
sc62w ---------------------9,572
sc52d ----------------------4,967

Fenix:
pd31-------------------------9,018
pd35vn----------------------22,582

Noctigon M43:
219b----------------------33,410
xpg s3 3d-----------------51,099

Results met my expectaction, except the Hyper Red HDS. Interestingly, it scored higher than xpg2. Although it does make sense since the red emitter is so tiny.

reppans · Jun 13, 2015

Nice.. for $5 in a hardware store, you can turn that smartphone Lux meter into a serviceable lightbox for measuring lumen output (clicky).

LessDark · Jun 14, 2015

Hm interesting, are you getting somewhat accurate measurements?
Which app are you using to measure lumen?

reppans · Jun 14, 2015

LessDark said:
Hm interesting, are you getting somewhat accurate measurements?
Which app are you using to measure lumen?

Assuming you are referring to me, I find smartphone light meters to be a rough guide, but far better than what you can discern with the naked eye. I've used DSLRs as well, and they have more precise light meters, but camera "stops" are not as granular. Both are relative meters, so "ANSI accuracy" also heavily depends on what (who) you choose to calibrate to. Both compare reasonably well to the results from my dedicated lux meter. I find both to be significantly more accurate than many popular manufacturers here though

. I use Pocket Light Meter (free app) on an iPhone.

TEEJ · Jun 14, 2015

Just a note to point out that lux is a weighted scale, and, if wavelengths are missing, such as is the case with a RED LED, so there's less green or blue or yellow, etc...the relative lux will be proportionally lowered as well.

Seattle Sparky · Jun 15, 2015

reppans said:
Nice.. for $5 in a hardware store, you can turn that smartphone Lux meter into a serviceable lightbox for measuring lumen output (clicky).

Nice idea, I will definetly give it a try.

Seattle Sparky · Jun 15, 2015

TEEJ said:
Just a note to point out that lux is a weighted scale, and, if wavelengths are missing, such as is the case with a RED LED, so there's less green or blue or yellow, etc...the relative lux will be proportionally lowered as well.

Then, is it surprising that red led scored max on the lux meters compared to other HDS's? May be the tiny led size and 1A drive level make up the difference?

Mr Floppy · Jun 16, 2015

Seattle Sparky said:
Then, is it surprising that red led scored max on the lux meters compared to other HDS's? May be the tiny led size and 1A drive level make up the difference?

More likely the sensor in the phone has an auto gain set too high. The sensors in the phone are not meant for measuring. Most aren't linear and most needed some sort of calibration that isn't just an offset.

markr6 · Jun 16, 2015

I've been playing with one - LuxMeter. It is OK for generalizations (is my light brighter with NCR18650B or Efest 20A?) But if you move the light or phone a fraction of a mm, it can skew the numbers big time. Plus it depends on what you're hitting with the beam (ceiling, piece of paper, wall) and distance from that object.

So, that PVC pipe idea is great! It would be a good idea to make some type of jig for the phone to set in, so it's always in the same spot. Again, the slightest movement can throw off your measurement.

TEEJ · Jun 16, 2015

Essentially, the phone's light meter is to allow setting of the screen brightness...so if its darker, the screen can be darker, and, if its brighter out, the screen can be brighter to compensate, etc.

Its not really meant to be a "light meter", but, as the electronics are about the same...the apps can tap into it and give a read out in lux, etc.

So, no - its not going to be linear or compensated, etc, and, will have gaps in performance, such as the angle sensitivity mentioned, etc.

As the apps are typically free, give or take some spam you may later suffer, etc...there's essentially real no downside to using a phone app as a light meter as long as you understand its limitations.

As lux is lumens per square meter, and a lumen is a weighted scale, based upon wavelengths that the human eye perceives better, etc, lights with greener hues score highest, and those with redder tones score lowest, etc. (We see green a lot better than red, etc)

So, a light with a red LED will be able to saturate the red part of the spectrum measured.

Now, as a phone's meter is NOT calibrated to read in lumens per se...it may NOT be weighted by wavelength and, may not actually BE measuring lux, because its not weighted as per the lumen proportions....and may be merely measuring intensity so as to adjust the screen, its built in meter's purpose.

So, the apps would ignore the weighting, as its a fine point that is, to most, an academic rather than a practical difference, and, the sensor itself is what is creating the original data...and the app would not be able to separate out the signal strength by wavelength.

That would mean that a red light's lux might be "measured" the same as a green light's lux of equal intensity.

reppans · Jun 16, 2015

TEEJ said:
Essentially, the phone's light meter is to allow setting of the screen brightness...so if its darker, the screen can be darker, and, if its brighter out, the screen can be brighter to compensate, etc.

Its not really meant to be a "light meter", but, as the electronics are about the same...the apps can tap into it and give a read out in lux, etc.

So, no - its not going to be linear or compensated, etc, and, will have gaps in performance, such as the angle sensitivity mentioned, etc.

As the apps are typically free, give or take some spam you may later suffer, etc...there's essentially real no downside to using a phone app as a light meter as long as you understand its limitations.

As lux is lumens per square meter, and a lumen is a weighted scale, based upon wavelengths that the human eye perceives better, etc, lights with greener hues score highest, and those with redder tones score lowest, etc. (We see green a lot better than red, etc)

So, a light with a red LED will be able to saturate the red part of the spectrum measured.

Now, as a phone's meter is NOT calibrated to read in lumens per se...it may NOT be weighted by wavelength and, may not actually BE measuring lux, because its not weighted as per the lumen proportions....and may be merely measuring intensity so as to adjust the screen, its built in meter's purpose.

So, the apps would ignore the weighting, as its a fine point that is, to most, an academic rather than a practical difference, and, the sensor itself is what is creating the original data...and the app would not be able to separate out the signal strength by wavelength.

That would mean that a red light's lux might be "measured" the same as a green light's lux of equal intensity.

Might be some confusion here...

The App for my iPhone5 uses the camera's auto exposure light meter through the lens on the back of the smartphone while the "light meter" used to auto adjust screen brightness is on the face of the smartphone. It's possible the same internal meter is used, but the lens is definitely different.

The way to use photography light meters (eg, smartphone apps and manual DSLRs) as a lumen meters (of course, assuming you have a consistent method for light collection, sampling and diffusion) is as a relative measurement vs a known calibration point.

In a very simple example, I can calibrate a known 100 lumen mode to 1/100th of a second shutter speed on an camera App or my DSLR. Then once calibrated, if I re-meter a 50 lumen mode for shutter speed, the App/DSLR should return 1/50th of a second as the correct exposure (half the light requires twice the exposure time). 500, 5, and 0.5 lms should meter 1/500ths, 1/5th, and 5/1 (or 5) seconds, respectively. You can key off shutter speed (photog apps) or lux (light meter apps), etc. - doesn't matter they are just linear measurements, as lumens are. EV (exposure value) can also be used for more granularity (if using photog apps/meters) although EV is a power function (but still has a simple conversion formula).

Mr Floppy · Jun 18, 2015

reppans said:
Might be some confusion here...

The App for my iPhone5 uses the camera's auto exposure light meter through the lens on the back of the smartphone while the "light meter" used to auto adjust screen brightness is on the face of the smartphone. It's possible the same internal meter is used, but the lens is definitely different..

I don't know if the fruit company does it but the android side of things has direct access to the numbers coming out of light sensor. Only some of the Android apps will use the camera to get the light as it requires more processing than just reading a simple number. In fact some apps that use the camera, will track certain areas so the focus of the light is all wrong. Centre spot is what should be used but some phones can't control that manually.

TEEJ · Jun 18, 2015

And to further clarify - there's no lumen meter - its a lux meter if anything.

As lux is lumens per square meter, the area sampled to get the lux will dictate the representativeness of the measurement.

If the meter's sensor is sampling a teeny point, it may, or may not, be a representative teeny point....so, a percentage of uncertainty is created.

And, sure, they could use the same processor for different input sources...or not. I haven't dissected the phones to see.

Pideas · Jun 20, 2015

Lux meter app? An app that measures lumens, at least with some accuracy, would be a lot more difficult because it would need some kind of hardware such as an integrated sphere.

Kestrel · Oct 5, 2015

Just a little bump for this thread to append a question I have;

I just installed the "Light Sensor" app for my new Android, and since it has a 'calibrate' function I'd like to take a crack at that. :-/
I don't have a known light source handy; sunlight is too variable, and most of my lights are either modded or oddball/atypical older lights (older-bin neutral Malkoffs etc) - so the lux they provide is relatively unknown.
I also understand that the wavelengths from my non-blackbody LED lights will be an additional challenge.

Any suggestions for calibrating something like this? It doesn't have to be perfect but I'm thinking that with just a little bit of effort I could improve on the lux readings it provides, thanks.

LedTed · Oct 5, 2015

TEEJ said:
And to further clarify - there's no lumen meter - its a lux meter if anything.

As lux is lumens per square meter, the area sampled to get the lux will dictate the representativeness of the measurement.

If the meter's sensor is sampling a teeny point, it may, or may not, be a representative teeny point....so, a percentage of uncertainty is created.

And, sure, they could use the same processor for different input sources...or not. I haven't dissected the phones to see.

In inclined to agree with TEEJ on this,

Yes, Lux meter.
and
The sensor / software is probably doing some sort of sampling. That sampling may not be representativeness of the true measurement.
(If I may also add, the sensor itself may be more sensitive to one color - i.e. red.)

But, using a cell phone as a light meter is fun to try and should give some idea.

more_vampires · Oct 6, 2015

LedTed said:
But, using a cell phone as a light meter is fun to try and should give some idea.

Our Star Trek Communicators are becoming Star Trek Tricorders! Dontcha just love the 21st century?

ForrestChump · Oct 7, 2015

reppans said:
Nice.. for $5 in a hardware store, you can turn that smartphone Lux meter into a serviceable lightbox for measuring lumen output (clicky).

lux meter android app results

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