Detecting PWM with a camera phone

I was playing with my iphone camera and wanted to see what the Klarus XT11's led looked like when it was on. I didn't expect it to detect PWM so easily.

Klarus XT11 - High


Klarus XT11- Medium -- (Heavy PWM?)


Klarus XT11- Low


Armytek Predator - High - No PWM

Interesting find. I noticed a similar effect with my Android camera when testing several of my lights including my Maratac AAA and my HDS.

I find that if I can't SEE the PWM while using the light, as it improves run time and performance, I'm glad its there.

When its too slow, so that the cycle is visible in use, THEN I don't want it.

Otherwise, its a GOOD thing.

I guess I'm old fashioned - I just use a ceiling fan or running water to detect PWM.

How do you get the screen print off the iPhone camera so it includes the buttons and GUI controls?

Chicken Drumstick said:

How do you get the screen print off the iPhone camera so it includes the buttons and GUI controls?

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Sleep + Home button

Very cool... I am confused as to why the whole screen has the lines running through it, as opposed to just the beam, but I tried it for myself and get the same effect. Interestingly very high frequency PWM does not show, like on the Quark Mini AA.

Kinda surprised that a light like that doesn't have any current regulation.

reppans said:

Very cool... I am confused as to why the whole screen has the lines running through it, as opposed to just the beam, but I tried it for myself and get the same effect. Interestingly very high frequency PWM does not show, like on the Quark Mini AA.

Kinda surprised that a light like that doesn't have any current regulation.

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I put my camera right up to the light's lens, which is why the lines are showing throughout the screen. I also tried my RRT-0, it has much lighter ripples instead of solid black lines. I don't know how to interpret any of these results though.

The RRT-0 is also PWM? Guess it doesn't mention anything about current control on their website. Wonder if SWMs rotaries are too (although it says "constant current control"... is that the same as current regulated?). I just assumed all these higher - end lights would be current regulated. :shrug:

Here's a Zebralight H51w on moonlight (one of it's PWM modes) taken on a 5mp new iPad though... Lines are faint and widely spaced, but I can see this light's frequency is quite low (easy to see by waving you hand in front of the beam).

reppans said:

The RRT-0 is also PWM? Guess it doesn't mention anything about current control on their website. Wonder if SWMs rotaries are too (although it says "constant current control"... is that the same as current regulated?). I just assumed all these higher - end lights would be current regulated. :shrug:

Here's a Zebralight H51w on moonlight (one of it's PWM modes) taken on a 5mp new iPad though... Lines are faint and widely spaced, but I can see this light's frequency is quite low (easy to see by waving you hand in front of the beam).

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I placed the camera directly on top of the light, aiming towards the emitter. I also checked my Quark mini 123, it has slight PWM on low and medium, but no visible PWM on high.

Here is a picture of the RRT-0 with slight PWM. I wouldn't be surprised if any other magnetic control ring lights show this type of PWM.

Yeah your right, you really need to be right on top of the emitter/head. Here's a retake of the ZL on moonlight, and below that the QAA mini on low. No evidence of the lines on my other lights known to be current controlled. Thanks for posting this, it seems like an excellent and definitive PWM test. :thumbsup:

aimxplode said:

I wouldn't be surprised if any other magnetic control ring lights show this type of PWM.

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So, anyone have a magnetic control ring light they can test? (or maybe it's better off not knowing the result ).

You can have constant current control and PWM at the same time. They are not mutually exclusive.

Semiman

SemiMan said:

You can have constant current control and PWM at the same time. They are not mutually exclusive.

Semiman

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So then, what's the technical wording to look for if you don't want PWM? I think 4Sevens and Zebralight uses "current regulated." And does that mean (in general) if a light doesn't specifically mention "current regulated" then it is using PWM? (like Jetbeam?)

Zebralight specifically states where it uses PWM.... I'm still confused whether or not SWM does.

(edit.... Think I see that the SWM "V" series is using PWM since their "M" series lights do use the wording "fully-regulated constant current.").

reppans said:

So then, what's the technical wording to look for if you don't want PWM? I think 4Sevens and Zebralight uses "current regulated." And does that mean (in general) if a light doesn't specifically mention "current regulated" then it is using PWM? (like Jetbeam?)

Zebralight specifically states where it uses PWM.... I'm still confused whether or not SWM does.

(edit.... Think I see that the SWM "V" series is using PWM since their "M" series lights do use the wording "fully-regulated constant current.").

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The current going into the LED during each pulse is regulated and fixed and PWM is simply a cheap way to control the modes. I guess the words you look for are things like linear regulation, regulated buck/book convertor etc. You can easily tell if a light uses PWM though, and it's VERY annoying at night as it feels like you've got a strobe light when you move around.

You don't need a camera. You need your eyes too look with, and a hand to move the light fast with. Just wave it in front of youre eyes really fast and look at the led.
Picture of the difference. DQG II (no pwm)vs Quark min-x (pwm makes the "dotted line").

All my current regulated lights have better runtimes than my pwm lights. (aaa vs aaa, aa vs aa etc.) My current regulated aaa lights can often have some days extra runtime compared with "normal" pwm aaa lights.

All my pwm lights have better tint in lo modes. (current regulated ones changes tint when in lo modes.)


Happy face with no pwm


Diden't move my hand fast enuff when drawing "smileys", but you can barly see the pwm in some spots on the angry face.

jorn said:

You don't need a camera. You need your eyes too look with, and a hand to move the light fast with. Just wave it in front of youre eyes really fast and look at the led.

Happy face with no pwm


Diden't move my hand fast enuff when drawing "smileys", but you can barly see the pwm in some spots on the angry face.

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Haha that's awesome, how did you get your camera to catch that? My arms would probably get tired after a while..

Shutter speed 6 sek. You have 6 sek to "draw your stuff" into the camera Should have used a light with slo pwm frequenzy, easyer to see the pwm with lo Hz. The red lines is me blocking the light with my tumb.

jorn said:

Shutter speed 6 sek. You have 6 sek to "draw your stuff" into the camera Should have used a light with slo pwm frequenzy, easyer to see the pwm with lo Hz. The red lines is me blocking the light with my tumb.

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I guess that's just the thing.... It is not easy to see high frequency PWM with your bare eyes, like Quark's Mini (I been waving a ruler in front of the beam). I can just barely make it out on water from the shower head. The cell phone pix is quick and easy and totally obvious.

I just wave my spread fingers back and forth in the beam as fast as I can. If I see way more than 5 fingers, it has pwm. If I just see 5 blurry fingers, then either there's no pwm, or the pwm frequency is fast enough that I won't notice it when I'm using the light, and is therefore not an issue.