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Thread: PWM - What is it, How does it work and how to detect it.

  1. #91
    Flashaholic* Cataract's Avatar
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    Default Re: PWM - What is it, How does it work and how to detect it.

    I'm pretty sure you have it cornered to the dropin. I'd take a chance and write Malkoff about this, they might just replace it.
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  2. #92
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Cataract, thank you for a simple to understand explanation. Excellent photos and graphics!

  3. #93
    Flashaholic* Cataract's Avatar
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Thanks, I did this all in the good spirit of CPF knowledge sharing :
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  4. #94

    Default Re: PWM - What is it, How does it work and how to detect it.

    First, thanks Cataract for a very informative description of PWM!

    Quote Originally Posted by LukeA View Post
    Or, using a photograph, you can calculate frequency by counting the number of pulses and dividing that number by the picture's exposure time in seconds. In the first image in the OP, there are 8 pulses shown in a time of 1/8s for ~64Hz.
    Great tip, this may be the easiest method to measure PWM with fair accuracy with just a camera. With this, I was able to find the PWM of an Everest headlight to be about 110 Hz, which I find quite annoying in some situations, while the higher PWM of Lumapower LM31 on low mode is higher at about 675 Hz, which is not that noticeable in most situations.

    Quote Originally Posted by jorn View Post
    The loudest light i have owned is a lumapower lm21. The noice from the pwm filled the room... The funny thing is i could hear it used way different frequencys on med and lo mode. Lo mode was growling in a lo pitch noice (crappy low frequenzy), medium mode was screaming in a higher frequency. A simple shaketest comfirmed it visually.
    Interesting, I bought a Lumapower LM31 recently, and there I can only hear a faint whine if I hold the light right next to the ear.

  5. #95

    Default Re: PWM - What is it, How does it work and how to detect it.

    Any frequency above 5kHz is pretty much undetectable, unless you're using a slow motion camera.

    Although, if the frequency is 1kHz, and the duty cycle is 5%, then 1/1000=0.001, and 100/5=20, and 0.001*20=0.02, and 1/0.02=50.
    So the light may appear to be flashing at 50Hz. Just thought I'd mention it.

    Nice explanation by the way.

  6. #96

    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by agnelucio View Post
    Although, if the frequency is 1kHz, and the duty cycle is 5%, then 1/1000=0.001, and 100/5=20, and 0.001*20=0.02, and 1/0.02=50.
    So the light may appear to be flashing at 50Hz.
    If that was the case, then my LM31, with a PWM frequency of 675 Hz and a duty cycle of 1% on low, would appear to flash at about 7 Hz, which it doesn't. It still appears to flash at 675 Hz, while during every flash cycle the light is only on for 1% of that time.
    Last edited by weaver; 10-29-2013 at 06:12 AM.

  7. #97

    Default PWM - What is it, How does it work and how to detect it.

    I think this thread should have a disclaimer "if you want continue enjoying all your lights, please do not read." Before CPF, I never knew what PWM was, and I never saw it. Then I learned what it was, started looking for it, and even found very easy ways to detect high frequency PWM in every day scenarios and without equipment.

    Damn it, now I can't stop seeing it and it has all but ruined my taste for any light with it. It doesn't make me nauseous or anything, but it constant comes into my view and my brain instantly notices something unnatural that makes me do a double take... "Oh yeah, PWM" and then everything is back to normal. It's just plain annoying now, and has made quite a few shelf-queens of some good lights.

    Ignorance is bliss.

  8. #98
    Flashaholic* Cataract's Avatar
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by agnelucio View Post
    Any frequency above 5kHz is pretty much undetectable, unless you're using a slow motion camera.

    Although, if the frequency is 1kHz, and the duty cycle is 5%, then 1/1000=0.001, and 100/5=20, and 0.001*20=0.02, and 1/0.02=50.
    So the light may appear to be flashing at 50Hz. Just thought I'd mention it.

    Nice explanation by the way.
    Thanks!
    I'm not 100% sure on your math, though (no time to pick up the calculator but I think you skipped a step), but yes, the shorter the duty time, the more it will appear to flash, mostly because it is easier to detect. I think the correct interpretation of your math is not really that it will look like it is flashing at 50Hz, but that it should be as easy to detect as if it was...

    Quote Originally Posted by reppans View Post
    I think this thread should have a disclaimer "if you want continue enjoying all your lights, please do not read." [...]
    LOL! I think you're right, though...

    Quote Originally Posted by reppans View Post
    [...]Before CPF, I never knew what PWM was, and I never saw it. Then I learned what it was, started looking for it, and even found very easy ways to detect high frequency PWM in every day scenarios and without equipment.

    Damn it, now I can't stop seeing it and it has all but ruined my taste for any light with it. It doesn't make me nauseous or anything, but it constant comes into my view and my brain instantly notices something unnatural that makes me do a double take... "Oh yeah, PWM" and then everything is back to normal. It's just plain annoying now, and has made quite a few shelf-queens of some good lights.

    Ignorance is bliss.
    I noticed that with medium speed PWM you can enjoy blissing ignorance for quite a while. With slow PWM lights, though, you notice it very easily and it becomes annoying over time when you get used to have lights with non-detectable or no PWM at all. I was lucky enough to notice it early, L0D being one of my first lights, and have paid attention from there on, even though it does not make me sick either, but I understand the pain or shelving a perfectly functioning light. I use my L0D as a keychain light now, and my older Zebras will become beaters when I upgrade them as they only annoy me near reflective surfaces.
    Last edited by Cataract; 10-29-2013 at 08:29 PM.
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  9. #99

    Default PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by Cataract View Post
    I noticed that with medium speed PWM you can enjoy blissing ignorance for quite a while. With slow PWM lights, though, you notice it very easily and it becomes annoying over time when you get used to have lights with non-detectable or no PWM at all. I was lucky enough to notice it early, L0D being one of my first lights, and have paid attention from there on, even though it does not make me sick either, but I understand the pain or shelving a perfectly functioning light. I use my L0D as a keychain light now, and my older Zebras will become beaters when I upgrade them as they only annoy me near reflective surfaces.
    Interesting... my old Zebra H51w uses a PWM that's about the slowest I've ever seen on any light - it was the first to become a shelf queen. The Foursevens Minis uses a high frequency, but just as you have mentioned here and elsewhere, the reflections off glass, faucets, etc, are what constantly catch my eye for that annoying double-take - I can't use them any more. It's really not an issue outdoors with few reflective surfaces, but indoors, there always seem to be something that reflects back.

    At a quick glance, I also didn't see any mention here of the cellphone PWM test. Here's an example of a current regulated 47s Quark, high frequency 47 Mini, and and low frequency H51w all taken with an iPhone (they're all on their lowest modes):


  10. #100
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    Default Re: PWM - What is it, How does it work and how to detect it.

    I notice outddors because it rains alot, so any wet surface can be reflective..
    Hate the pwm flicker on tail lights on the newer cars. Slow pwm led lights should have been banned on cars. The faster the car in front of you moves, the more visible the pwm gets. In every curve, or bump in the road, the flicker from the tail lights grabs my attention. The roads around here are made of bumps and curves only

  11. #101
    Flashaholic* Cataract's Avatar
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by reppans View Post

    Coool! That's a great visual!

    Quote Originally Posted by jorn View Post
    I notice outddors because it rains alot, so any wet surface can be reflective..
    Hate the pwm flicker on tail lights on the newer cars. Slow pwm led lights should have been banned on cars. The faster the car in front of you moves, the more visible the pwm gets. In every curve, or bump in the road, the flicker from the tail lights grabs my attention. The roads around here are made of bumps and curves only
    ...and also whenever you move your eyes around...ach! I do everything to avoid them; slow down, pass them or just take another street when possible. I do see less of them lately, but the age of darkness is upon us; what normally is a good time for flashaholism now has it's demon! I did notice that the worst ones (I prefer not to name the 2 specific brands here) seem to have remedied to that on newer models, but other makers are making the same mistake all over again. Hopefully there will be a law against that sometime soon... hopefully.
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  12. #102

    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by mhphoto View Post
    Here's a picture I took of a 123≤ Tactical (R2) before I sent it back because the flickering was so bad.



    On the left is "moonlight mode", middle is "low", and on the right is "medium". "High" and "max" showed no flickering.

    After I got so fed up with the flickering I sent it back and got the S2 123≤ Turbo, which as I said, flickers on the "medium" level. My 123≤ Tactical warm white flickers on "low" and "medium", and my RGB neutral flickers on "moonlight".

    I have a Mini AA and its PWM is much higher frequency than the flickering coming out of the Quarks.

    From what I remember about the thread that discussed this issue, the flickering is not so much a sharp "on and off" cycle, but rather an "on and fade" cycle.
    Quote Originally Posted by Cataract View Post
    Nice picture! that's almost art, but what is shown here is definitely PWM. I have never seen such bad PWM on any of my 4sevens lights, but there are people who could say a lot more about 4sevens and the use of PWM.
    Could that be a failed storage device (blown cap or inductor overheated and short cct) in the switching regulation ?

  13. #103
    Flashaholic* Cataract's Avatar
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by Yagon View Post
    Could that be a failed storage device (blown cap or inductor overheated and short cct) in the switching regulation ?
    Yes, it could be a blown or defective component (also including frequency pulser), bad solder or cracked board whether the problem was from manufacturing, shipping/handling, overheat of even freeze. I dropped my 4 sevens lights many times with no such issue though, so I tend to think it was a defect from the manufacturing side. This kind of problem might be hard to catch during QC since the light generally behaves the way it should.
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  14. #104

    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by Cataract View Post
    Yes, it could be a blown or defective component (also including frequency pulser),
    Do you mean the cmos switch ?
    Thought that would either fail open or closed cct .
    Doesn't have to mean a manufacturing error(of the flashlight) too , it could simply be a case of infant mortality of the component .
    Last edited by Yagon; 11-05-2013 at 03:48 PM.

  15. #105
    Flashaholic* Cataract's Avatar
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by Yagon View Post
    Do you mean the cmos switch ?
    Thought that would either fail open or closed cct .
    Doesn't have to mean a manufacturing error(of the flashlight) too , it could simply be a case of infant mortality of the component .
    Yes; I've seen CMOS and other types of clocks ticking at the wrong rate because of manufacturing defects or because the signal wasn't steady enough (because of a manufacturing defect again) for other circuits to function normally and even because of premature death of only part of the IC. Most of the time things are black and white with modern IC's, but not always...

    And yes again, it could be premature death of some component. 4Sevens is not necessarily to blame on this, but a faulty solder or trace could possibly cause this type of problem too; I've seen weird stuff in my career. Without their blueprints on hand it is hard to rule out anything for sure, and even then... That's why manufacturers usually want to have the defective product back; so they can find out what went wrong and prevent it from happening again.
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  16. #106

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    I don't think that dropping a light would cause significant damage to the electronics (except perhaps for a large inductor). Much more likely to be a dry/dodgy solder joint.

  17. #107

    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by Cataract View Post
    ..the correct interpretation of your math is not really that it will look like it is flashing at 50Hz, but that it should be as easy to detect as if it was...
    Yes, sorry, that's exactly what I meant. (and should have said).

  18. #108
    Flashaholic* Cataract's Avatar
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by agnelucio View Post
    I don't think that dropping a light would cause significant damage to the electronics (except perhaps for a large inductor). Much more likely to be a dry/dodgy solder joint.
    Very likely, but I've seen stuff happen. Since we do not know what was the actual cause, we can only propose theories which is not the scope of this thread (my bad for digressing so far out). Let's get back on track with PWM

    Quote Originally Posted by agnelucio View Post
    Yes, sorry, that's exactly what I meant. (and should have said).
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  19. #109

    Default PWM - What is it, How does it work and how to detect it.

    Just read through this. Excellent write for me. I was wondering about this and now it's clear. Thanks so much!


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  20. #110
    Flashaholic* Cataract's Avatar
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Thanks Steve. Knowing I could make it clear for fellow CPFers makes my day
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  21. #111
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by afdk View Post
    PWM can be easily seen by pointing your light at your shower head, with water running of course! The water may look like separate drops depending on the PWM frequency. My Pelican 9410 does use PWM for the lower mode, but it is of sufficient frequency that it's only noticeable in the way described.

    Try this with your lights, let me know what you see.
    I tried this with 5 four lights: Draco (Flupic), Haiku (GDuP, 4 level), Mac's Tri-EDC, Jetbeam TC-R1, & P60 dropins for my TnC from Vinh and Nailbender... The Draco with Flupic had the worst PWM on low and user defined settings.. Very choppy... On high, there was no PWM... The Haiku with the GDuP driver had no perceptible PWM on any level except some slight "chaining" at 10 ma... At 200 ma all the way up to 1200 ma, there was no PWM... The TC-R1 had no PWM at any level, even the very, very low settings had no PWM... Mac's Tri-EDC and the P60 dropings from Vinh and Nailbender behaved exactly the same.. High quality, high frequency PWM at low and medium levels and no PWM on high... The PWM at these lower levels was excellent, just some high speed "chaining".... This experiment really makes me appreciate the GduP driver and the TC-R1 driver... Thanks for the tip !!

  22. #112
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by hjdca View Post
    This experiment really makes me appreciate the GduP driver and the TC-R1 driver... Thanks for the tip !!
    Actually, I am more impressed with the GDuP than the TCR1 because of the buck, boost drivers... The GDuP will do its thing with a primary and a rechargeable... The TCR1 does not have this capability and you have to use a rechargeable... Other DC engines from China also seem to be missing buck drivers..., ie. you put a 4.2 volt rechargeable in it and all you get is high, like Fenix...

  23. #113
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by Yagon View Post
    Could that be a failed storage device (blown cap or inductor overheated and short cct) in the switching regulation ?
    Check my post at the end here, along with others observations:

    http://www.candlepowerforums.com/vb/...PWM&highlight=

    This is more than one or a few lights with bad components, and David considers it normal, and not PWM. It is apparantly "warble" in a constant current controlled circuit. It is interesting as it seems to be the only case of a non-PWM controlled light looking exactly like a PWM light, and at a fairly low frequency. The reduction to 30% brightness rather than 0% as in true PWM does not seem to lessen the effect noticeably. Just when you thought you were safe from flickering lights by ordering a 100% current controlled light, there comes an exception.

    My interest in the other thread centers on the different flavors of this circuit. Most Pro interfaces seem steady, but I have one that all three of the lowest levels do it. Most reports are for the Tactical interface, and only on the low and medium. But there are also plenty of the same lights without the phenomenon.

  24. #114
    Flashaholic* Cataract's Avatar
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Thanks Hondo, I was just about to point to that resuscitated thread. Even though the flickering effect in Quarks is not supposed to be PWM per se, our eyes perceive it as the exact same phenomenon and the effects on perceived light intensity will obey the same law of average output. Usually, though, this flickering in Quarks is very high frequency (at least in all of my numerous Quarks) and very hard to see, as pictured in my original post:



    Anything significantly noticeable sounds unusual to me and I too would find it very annoying.
    Last edited by Cataract; 11-29-2013 at 06:22 PM.
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  25. #115
    Flashaholic* Hondo's Avatar
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    Default Re: PWM - What is it, How does it work and how to detect it.

    I managed to grab this image of three lights. The one on the left is my Quark 123^2 Tactical, wearing a filter to remove green and make it more neutral. The center is an ITP A2 Eos, known to be in the 2K+ Hz range. The last is the notorious 100 Hz Fenix L0D. They are all on their medium level.




    I would give the Quark, based on the Fenix being 100 Hz, about 350 Hz. I somehow don't get the graph linked by cave dave in the other thread, as it shows a full cycle in what is labeled about 0.5 ms, which would be 2 kHz. Yet he says it supports his guess of about 200 Hz. That was measured by HKJ, and I am guessing it is the non-objectionable artifact that David speaks of in a light which does not exhibit this "PWM-like" behavior.

    Here is another pic with just the Quark, in which I really cranked up the speed I swept the light. This emphasizes that the brightness is indeed not going to zero, just getting a lot dimmer, so this is not PWM. On the Fenix, it is clear that the light goes completely dark between cycles.


    Last edited by Hondo; 08-03-2017 at 04:21 PM.

  26. #116

    Default PWM - What is it, How does it work and how to detect it.

    I get a similar thing with my D25A clicky on moonlight mode, but only with a low battery. However, I also have another copy that has this PWM-like behavior with fresh cells. Here's an old picture of it next to a Quark AAX... (FWIW, I have many LV head Quarks, and one HV, and have not noticed any PWM-like behavior.)


  27. #117

    Default Re: PWM - What is it, How does it work and how to detect it.

    FWIW, particularly in large LED replacements for incandescent in luminaires, the presence of a phosphor for CRI improvement can partially mask the PWM. The relaxation time of the phosphor can be greater than the period of the pulses.

    Tapatalk...

  28. #118
    Flashaholic* Cataract's Avatar
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    Default PWM - What is it, How does it work and how to detect it.

    Great pics guys! I really like the idea of holding multiple lights together so you can have a fairly precise number on frequency based on a known one (provided you take the time to count all the bright spots)

    Quote Originally Posted by inetdog View Post
    FWIW, particularly in large LED replacements for incandescent in luminaires, the presence of a phosphor for CRI improvement can partially mask the PWM. The relaxation time of the phosphor can be greater than the period of the pulses.

    Tapatalk...
    Excellent to info. Never even thought of that.




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  29. #119

    Default Re: PWM - What is it, How does it work and how to detect it.

    current-controlled, PWM nice explained thanks
    My Sipik SK68 is not CC or PWM, is it possible to update it ?

  30. #120
    Flashaholic* Cataract's Avatar
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by KARADENIZ View Post
    current-controlled, PWM nice explained thanks
    My Sipik SK68 is not CC or PWM, is it possible to update it ?


    Thanks! I will add one or two things to the original post eventually, but for now I'm still unboxing stuff.

    I'm not familiar with the Sipik as I don't own one or ever seen one in person. Try in the "homemade and modified flashlight" section; Almost every flashlight has been modified by someone at some point
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