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

  1. #271
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    Default Re: PWM - What is it, How does it work and how to detect it.

    There are a several things to consider about whether a light is going to bother you, one is modulation depth (how deep the flicker is), the other is frequency of the flicker, and the shape of the flicker can come into play as well.

    - The fluorescent lights that bothered you were likely old magnetic ballasts, who flickered at 100 or 120Hz. They did not turn on/of, but they would have peak-peak flicker up to 50% of the average. I.e. they went from 75% - 125% light output
    - Electronic fluorescents may have flicker at 100/120Hz, but it may only be 5-10%, and then riding on top of that may be flicker at 20+KHz which is invisible
    - CFLs are usually pretty similar
    - LEDs for the home are all over the map
    - The one in the hotel may have been a so-called AC drive LED which really does turn on/off at 100/120Hz. They are headache machines. Other LED lights for the home typically have anywhere from near 0 to 40-50% flicker, with the bulk it seems in the 20-30% range though as LEDs get more efficient, companies are willing to sacrifice a bit of efficiency for light quality.

  2. #272
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Accidental double post

  3. #273

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

    Quote Originally Posted by SemiMan View Post
    LEDs for the home are all over the map… headache machines
    Are there ANY home LED lighting systems you know of that dont use Pulses? I removed my Phillips Hue due to the PWM. It did not give me headaches, but the light seemed to make for a "fuzzy" ambiance. (no idea how to quantify that impression)

  4. #274
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by jon_slider View Post
    Are there ANY home LED lighting systems you know of that dont use Pulses? I removed my Phillips Hue due to the PWM. It did not give me headaches, but the light seemed to make for a "fuzzy" ambiance. (no idea how to quantify that impression)
    GE bright stick. I have a dozen around the house. No noticeable PWM at all.
    I Got tired of looking for the light at the end of the tunnel so i lit that bitch up myself! Convoy s2 365nm, Maxa-Beam Gen II, 55w hid/100w incan Vector Twin, Amondotech n30, vss-3A, Reylight Ti Lan v3, Helius Sigma 9, astrolux s41 219, Shadow JM35, BLF GT,

  5. #275
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    Default Re: PWM - What is it, How does it work and how to detect it.

    nice post !

  6. #276

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

    Quote Originally Posted by SemiMan View Post
    There are a several things to consider about whether a light is going to bother you, one is modulation depth (how deep the flicker is), the other is frequency of the flicker, and the shape of the flicker can come into play as well.
    Thanks for the rundown.
    You mention fluorescents, CFLs and LEDs all have flicker.
    What about incandescent, do they flicker too?

    Quote Originally Posted by FRITZHID View Post
    GE bright stick. I have a dozen around the house. No noticeable PWM at all.

    thanks, I looked it up,
    they are rated for 80CRI..
    no "noticeable" PWM? Have you tried taking a cell phone photo?

    For home lighting, Warm White incandescent with 100CRI and no? PWM are sounding better and better to me.
    Last edited by jon_slider; 02-28-2016 at 01:24 PM.

  7. #277
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Home LED lighting does not have PWM almost as a rule. The flicker is from the 50/60Hz line frequency and circuit\cost tradeoffs.

    Incandescent does flicker, just not a lot.

  8. #278
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    Default Re: PWM - What is it, How does it work and how to detect it.

    I apologize ahead of time. I didn't read all 270+ pages before replying so if it's been mentioned before, I'm sorry!

    I work as an electrical specialist with the engineering department at a large university. One thing we had noticed is an inconsistency between products that were supposed to be the same item but the flicker was different. What we found was that manufactures were changing suppliers of the LED drivers. I'm sure cost was their reasoning but the result was that the PWM frequency (in the case of motor control VFD's, we call it switching frequency) was different.

    Interesting stuff. Thanks for all of the info!

  9. #279

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

    Quote Originally Posted by SemiMan View Post
    Home LED lighting does not have PWM almost as a rule.
    thanks for your comments :-)
    Last edited by jon_slider; 03-02-2016 at 03:59 PM.

  10. #280
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    Default Re: PWM - What is it, How does it work and how to detect it.

    PM to jon slider.

    Bill

  11. #281

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

    Compare and contrast LED, Incandescent and Daylight tints, as seen by iPhone 5:

    Pic 1. Phillips Hue Tri LED home lighting system (91 CRI Pulse Width Modulated) 3000K
    Pic 2. 53 Watt Incandescent (100 CRI House Electric) 3000K
    Pic 3. Daylight inside, 12 noon, partly cloudy (100CRI sunlight) ~6000K





    And the LED assortment I use at different times of day, photo taken also at 12 noon with overcast sun
    XPG2 6000K, N219b 4000K, XPG 3000K (all drivers use NO PWM)
    Note the Nichia produces the most realistic Tint match in the color of the Buckskin

    Last edited by jon_slider; 03-07-2016 at 02:08 PM.

  12. #282

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

    Great PWM write up! :-)
    I am happy to realize how happy I am. Thus, a chain reaction of happiness.
    SkyLumen54@gmail.com




  13. #283

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

    An example of PWM from an older Maratac, as seen by a video camera (latest models have NoPWM)
    https://youtu.be/2jL7TiIQ4yM?t=4m39s
    Last edited by jon_slider; 05-04-2016 at 03:20 PM.

  14. #284
    Flashaholic* RI Chevy's Avatar
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Cool video of PWM

  15. #285

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

    5 seconds of PWM from a McGizmo Haiku:
    https://youtu.be/WzcRy1SYJd8?t=7m45s
    Last edited by jon_slider; 05-04-2016 at 04:00 PM.

  16. #286
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Nicely explained. I'm learning a lot just by looking around this forum

  17. #287

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

    Hi there!
    I think I found a better way of detecting PWM and even beeing able to estimate the dutycycle!
    Today everybody has a smartphone. So just open your camera app and turn on your light and point it as close as possible into your camera. (I don't know how bright the light can be to not kill the sensor, mine camera did 1W just fine). Then you see something like a black pic with white ,regularly appearing stripes(you can see a few of them at once at your screen), depending on your frequency slowly moving to one side. You can estimate the dutycycle from the width of the stripes. I saw that the stripes got more shallow on my minimaglite LED when I switched it into 25% mode.Post some pictures of it if it is working with your Phone's Camera.
    have fun
    PS: I could see these stripes up to somewhere about 800 HZ.
    Lights: AA LED Maglite, 3D LED Maglite, working on own flashlight

  18. #288

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

    > I could see these stripes up to somewhere about 800 HZ.

    I hope you post a photo

    I also use my phone


    this is how I use a piece of printer paper to compare beams. I no longer own any PWM lights, because the interfere with my photos

  19. #289

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

    Im bringing these forward to help someone who asked in another thread, "How Can I detect PWM?"

    Quote Originally Posted by reppans View Post
    [Eagletac]D25A on 3lms on the left. On the right is a 47s Mini - these are the two fastest PWM lights I've seen - this sweep is as fast as I can move my arm. [middle light is a known NoPWM control]



    ...
    the definitive way to tell is a fast sweep across a DSLR on time exposure, side-by-side with a known fast PWM light, and a true CC light (as above). My own eye-ball detection method is catch the spill in a reflection/mirror and move my eyeballs left to right quickly - I can quite easily see the PWM on the 47s Mini, but it is very hard to detect it on the D25A.
    Quote Originally Posted by jon_slider View Post
    A new way to detect PWM, use the spin cycle
    see the 4minute 15second mark…
    https://youtu.be/lwfAKmlbv7w?t=4m15s
    Quiz, why are there dots, instead of a constant streak of light?:-)
    -----
    Originally Posted by Cataract
    wave your light in front of your face. NOW, PWM will be easiest to detect on you light’s lowest mode ...
    you don’t need to send the lights directly into your eyes... just hold it so you can see the light on the side of the reflector as such:

    Turn the lights down if necessary, so you can see the light clearly enough and now wave it sideways like this:
    This is a picture of a constant current light. Any of your lights on maximum current should look exactly like that. [no dots, just blurry streak]


    Here’s a picture of [slow] PWM:


    Here is what “[fast]” PWM looks like:


    ----

    Quote Originally Posted by jon_slider View Post

    My iPhone sees the PWM much more obviously than my naked eye. Both lights are on Medium in this next photo:


    Neither light has PWM on high:


    When I wave the lights, the PWM is more obvious to my naked eye, than to the camera.
    Other ways to see the effect of PWM
    Shine the light at a stream of water from a faucet, or shower. The PWM light will freeze the drops in midair, kind of entertaining. Similar in Snow.

    Shine the light at the fanbelt of a car, the PWM light will seem to "stop" the belt, similar to a timing light. This also works on spinning things, like fan blades.

    I find my iPhone is quite good at finding PWM if I fill the screen with the light or shoot close range. Waving also works well, its just harder to photograph.

    Video also shows PWM in some exposures or angles
    McGizmo Haiku:
    https://youtu.be/WzcRy1SYJd8?t=7m45s

    An older Maratac:
    https://youtu.be/2jL7TiIQ4yM?t=4m39s
    Last edited by jon_slider; 07-05-2016 at 11:32 PM.

  20. #290
    Flashaholic* neutralwhite's Avatar
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Is 4500hz PWM an issue?.
    this is in relation to a pflexpro Nichia drop in I'm considering buying ?.
    avoid?.
    thanks!.
    Zebralight SC600 MkIV, SC52w.

  21. #291

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

    I have never heard of such a thing, good info

  22. #292
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by neutralwhite View Post
    Is 4500hz PWM an issue?.
    this is in relation to a pflexpro Nichia drop in I'm considering buying ?.
    avoid?.
    thanks!.
    For me, and 99.XX% of people, no.

    Can you still tell it from a non-PWM light if you go looking for it? Yes.

    Would I buy it? Yes. Once you get over ~1000 Hz, I don't let that influence my decision at all. And I can tolerate using some of my older lights with 100 - 200 Hz PWM, although I see it a lot in use.

  23. #293
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Quote Originally Posted by neutralwhite View Post
    Is 4500hz PWM an issue?.
    this is in relation to a pflexpro Nichia drop in I'm considering buying ?.
    avoid?.
    thanks!.
    I have noticed flicker on my budget flashlighs.
    I did a photo in my shower with 1/400s and could spot 11 bright and one fade point, so it is probably 4500Hz PWM.

    Now I am questioning how I can see flicker at my stillstanding flshlights, on old TV´s or PC Moniotors flicker stopped at 75Hz, 60Hz was a no go for me.


  24. #294

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

    fwiw, It has come to my attention that some lights that technically do not use PWM, because the Pulses do not drop all the way to Zero, are also NOT Constant Current. My goal in posting this is to eliminate the impression that just because a light does not use PWM, it does not mean it necessarily does not use Pulses that can interfere with Photos.

    Examples of lights that do not use PWM by the technical definition, but also are not Constant Current lights, include HDS, Zebralight, Eagletac, and Nitecore lights, that use Pulses that dont drop all the way to zero. More details in these threads:
    List Lights that use PWM and or Pulses that are NOT True Constant Current Lights
    List Lights that use NO PWM and ARE True Constant Current lights.

  25. #295
    Flashaholic* Hondo's Avatar
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Some of my high voltage Quarks exhibit this behavior too. But not all have it. David called it "circuit warble" .

  26. #296

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

    when im using pwm in flashlight with frequency around 1khz, there is buzzing noise. so i decided to use high frequency pwm around 20 khz and the noise is gone.

  27. #297
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Malkoff M361 uses a flicker rate of 310 Hz. I tries really hard to detect it. No luck with water yet, faucet.
    Will try the belt in the car next.

    I think there is a threshold where you cannot see PWM. 100 Hz I might see, 300, not. The statement I can see PWM is meaningless because it does not qualify the frequency.
    ****** Malkoff Devices ****** “Learn to light a candle in the darkest moments of someone’s life. Be the light that helps others see; it is what gives life its deepest significance.” ― Roy T. Bennett, The Light in the Heart

  28. #298
    Flashaholic* RI Chevy's Avatar
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    Default Re: PWM - What is it, How does it work and how to detect it.

    Just for the record, as I have previously stated several times. I have 3 M361N's, all of them display PWM on low, and I have the audible whine on low and medium. My eyes and ears can detect it.
    With that said, I really like the drop in. Tint is very nice.

  29. #299

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

    Quote Originally Posted by etc View Post
    Malkoff M361 uses a flicker rate of 310 Hz. I tries really hard to detect it. No luck with water yet, faucet.
    Will try the belt in the car next.

    I think there is a threshold where you cannot see PWM. 100 Hz I might see, 300, not. The statement I can see PWM is meaningless because it does not qualify the frequency.
    PWM is very difficult for most people to detect. There are also lights that produce "noise" that is technically not PWM, but still causes sensitive people to get migraines, such as Zebralight.

    when waving a light does not show PWM, even when we know from Malkoff that it is there, another technique that sometimes works is:
    taking an extreme closeup of the LED,
    see this post #76 that discusses this photo of a Zebralight:


    "noise" is very difficult to photograph, the camera has to be really close, and at just the right distance.
    Video closeups can also show "noise", but again it only works at just the right distance.

    imo, it is pointless to argue whether PWM matters or not, if someone does not notice it.
    for me, if the light has PWM, or pulses that produce "noise", then it is not Constant Current.
    I leave it up to each individual to decide if PWM or "noise" is acceptable.

    many, if not most, LED lights use PWM or pulses that produce "noise". Some people get very hostile about being told about it, and make all kinds of excuses why it does not matter to them, and should not matter to me. Im not going to argue about whether PWM matters to me, or someone else, because the conversation becomes hateful and unproductive. Many people Love their Zebras, HDS, Malkoff, etc, and they dont care about "noise" or PWM. So I just report what I find, without expecting to change hearts and minds.
    Last edited by jon_slider; 01-24-2017 at 02:18 PM.

  30. #300
    Flashaholic* Hondo'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 etc View Post
    Malkoff M361 uses a flicker rate of 310 Hz. I tries really hard to detect it. No luck with water yet, faucet.
    Will try the belt in the car next.

    I think there is a threshold where you cannot see PWM. 100 Hz I might see, 300, not. The statement I can see PWM is meaningless because it does not qualify the frequency.
    If it does not bother you, just enjoy.

    I have no problem finding 2,000 Hz PWM when I go looking for it, and I can show it to others as well. I only use the method of holding the light on about a 45 degree angle so I can see into the reflector from the side, and whipping it up and down looking for the "dotted line" of light (as in many photos above, including mine).

    Personally, I can use a 100 Hz light. When I move about, I am aware of the strobe-like effect, but it does not give me a headache or anything. But both my wife and I find the 100 Hz PWM LED car tail lamps irritating while driving at night.

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