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Thread: How to tell if your flashlight uses PWM or not

  1. #1

    Default How to tell if your flashlight uses PWM or not

    Turn off your bathroom lights and close the door. Turn on your flashlight and run the shower. If the water looks like a flickering string of beads, then your flashlight is using PWM. If its just a blur of water then it's current controlled.

    Noticed that when my bathroom light went out and I had to shower by flashlight.

    Jeff
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    Default Re: How to tell if your flashlight uses PWM or not

    Thanks for the info! I have not read too much negative threads about PWM on lights unless it is loud. I can see why some people might be displeased by this. I have one with a faint whine that I am happy with.

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    Flashaholic* subwoofer's Avatar
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    Default Re: How to tell if your flashlight uses PWM or not

    Another very easy method is to stand in front of a mirror or large glass window, but a several metres away, so that you can see the reflection of the reflector of the torch while it is turned on (don't point it straight at you) and then wave it around. If the light trail (due to your eyes persistent perception) is unbroken there is no PMW, if the trail appears to have breaks in it the there is PMW.

    I sometimes do this without a mirror, squinting so as not to be blinded.

    This can also give you an indication of the PWM frequency, lower frequency having bigger breaks and higher having smaller breaks.
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    Flashaholic* subwoofer's Avatar
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    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by ragweed View Post
    Thanks for the info! I have not read too much negative threads about PWM on lights unless it is loud. I can see why some people might be displeased by this. I have one with a faint whine that I am happy with.
    A light whining is not an indication of PMW, it is the driver circuit boosting voltage.

    PWM is where the light output is flashing in order to achieve a higher perceived brightness for a lower power output, or by cheaper lights often to achieve the lower levels rather than using proper current control.
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    Flashaholic* Launch Mini's Avatar
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    Default Re: How to tell if your flashlight uses PWM or not

    I have one that uses PWM, I like using it during heavy rain fall , the falling rain looks pretty cool.

  6. #6

    Default Re: How to tell if your flashlight uses PWM or not

    Not to sound stupid but what is PWM an is it good or bad ?

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    Flashaholic* subwoofer's Avatar
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    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by bassdawg View Post
    Not to sound stupid but what is PWM an is it good or bad ?
    Pulse Width Modulation

    Instead of a stead output of light, it is flashing very quickly and gives an apparent increase brightness for a particular power consumption when compared to a steady output (due to the persistence of vision - your eyes cannot detect very fast changes). Often the output level is controlled using PWM instead of controlling the current to the LED.

    I'm sure there are a load of threads explaining in more detail, but that is it in a nutshell.

    Is it good or bad?

    Well if the frequency is too low it can be very annoying and visible in your peripheral vision. - Bad

    It should give apparently higher output for a longer time (as it saves power by flashing the output instead of maintaining a constant output). - Good

    It can give unwanted strobing affects as described with the rain water or shower. - Bad

    It is neither good nor bad, but should be considered a feature which you may or may not want.

    Bear in mind that all old style TVs (CRT type) flash and the effect of persistence of vision makes the final picture appear steady. These TVs typically showed 25-30 frames per second, so flashed at this frequency 25-30Hz. Even new flat panels LCD / Plasma etc flash although the frequency is usually around 100Hz. So you have experienced a similar effect to PWM
    Last edited by subwoofer; 01-16-2012 at 10:50 AM. Reason: extra comments added
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    Default Re: How to tell if your flashlight uses PWM or not

    If u don't want to run the shower to check there's another watery method.... Pee thru the beam!
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    Default Re: How to tell if your flashlight uses PWM or not

    When we had blackouts, it was fun using flashlights w/ PWM to take a shower with.

  10. #10

    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by bassdawg View Post
    Not to sound stupid but what is PWM an is it good or bad ?
    Full power a certain % of the time (PWM) instead of partial power all the time (current controlled).

    PWM with a low frequency is often visible with the eye and can be nauseating.
    PWM with a high frequency is not visible to the eye, but is electrically less efficient than current-control.
    PWM does not cause LED's to tint shift (turn green/purple/whatever) at lower output levels like current control does.

    They each have their place, though I think everyone will agree that there's no place for low frequency PWM in a flashlight.

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    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by calipsoii View Post
    They each have their place, though I think everyone will agree that there's no place for low frequency PWM in a flashlight.
    +100! I hate very low frequency PWM and may sometimes cause headaches for me. So far PWM has been quite acceptable on all my lights with the exception of the Thrunite 2C which is so bad I had to return it back to GG. I felt bad when doing so but I just cannot accept the very low PWM.

    Anyway, one way I test a light for PWM is to shine it on a spinning fan. If there is PWM present it should be very obvious looking at the reflections. The other way would be to use the live view function on my digital cameras. If I see a row of dotted lines moving across the screen then it is an indication of PWM at work.
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    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by pjandyho View Post
    test a light for PWM is to shine it on a spinning fan.
    i dont think that our household has a fan.
    anyone with a youtube video demonstrating the fan vs. PWM trick?

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    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by shelm View Post
    i dont think that our household has a fan.
    anyone with a youtube video demonstrating the fan vs. PWM trick?
    Depending on the speed of the fan blades, you might not be able to tell if your flashlight has PWM

    I have made a thread explaining PWM in detail and the best ways I found to detect it:
    http://www.candlepowerforums.com/vb/...w-to-detect-it.

    subwoofer has a nice trick with the mirror, but at a distance I suspect you might not be able to detect higher frequency PWM like the Quarks use.
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    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by subwoofer View Post
    Pulse Width Modulation

    Instead of a stead output of light, it is flashing very quickly and gives an apparent increase brightness for a particular power consumption when compared to a steady output (due to the persistence of vision - your eyes cannot detect very fast changes). Often the output level is controlled using PWM instead of controlling the current to the LED.

    I'm sure there are a load of threads explaining in more detail, but that is it in a nutshell.

    Is it good or bad?

    Well if the frequency is too low it can be very annoying and visible in your peripheral vision. - Bad

    It should give apparently higher output for a longer time (as it saves power by flashing the output instead of maintaining a constant output). - Good

    It can give unwanted strobing affects as described with the rain water or shower. - Bad

    It is neither good nor bad, but should be considered a feature which you may or may not want.

    Bear in mind that all old style TVs (CRT type) flash and the effect of persistence of vision makes the final picture appear steady. These TVs typically showed 25-30 frames per second, so flashed at this frequency 25-30Hz. Even new flat panels LCD / Plasma etc flash although the frequency is usually around 100Hz. So you have experienced a similar effect to PWM
    PWM allows something other methods cannot match:

    longer battery life
    consistent color from the LED


    other known ways to modulate lumens, will always change the LED tint or color, and reduce runtimes

    so, there are benefits to PWM which cannot be ignored, but some people use the lights in situations
    where they notice the PWM flicker and find it annoying. there is a tradeoff to everything.

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    Flashaholic* pjandyho's Avatar
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    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by 127.0.0.1 View Post
    longer battery life
    consistent color from the LED
    Whilst I am sure you are right about the consistent color part, how does PWM equates to longer battery life? I am afraid I am clueless when it comes to this. Could you please enlighten me a little? Thanks!
    The love of light is the reason why I don't walk in darkness. But darkness has it's beauty...Sadly, my lights are much more beautiful!!
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    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by Cataract View Post
    might not be able to detect higher frequency PWM like the Quarks use.
    The regular Quarks are current controlled, not PWM controlled, am i right/wrong?

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    Default Re: How to tell if your flashlight uses PWM or not

    It's no problem to see the pwm, even on the quark minis. Shine it in ur face and shake it fast, big movments. Watch the led and you'll see it in med and lo mode. The higher frequency, the faster you need to move the light to see the effect. I also see the (strobe) effect when i walk fast past shiny/reflective stuff. Kind of annoying and grabs my attention every time when im out fishing or walking near water. It's no deal breaker for me, but i prefer no pwm. Tint shift, i can live with that.

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    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by shelm View Post
    The regular Quarks are current controlled, not PWM controlled, am i right/wrong?
    I can't remember for the life of me if it is the regular/tactical quarks or just the mini's or both. I'll have to check again when it's dark, because they use such high frequency PWM that it is very very hard to detect
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    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by pjandyho View Post
    Whilst I am sure you are right about the consistent color part, how does PWM equates to longer battery life? I am afraid I am clueless when it comes to this. Could you please enlighten me a little? Thanks!
    circuits that provide steady power to the led must resist some of that power to in order to dim it,
    this creates some heat in the resistance circuit and eats power that otherwise could go to producing light

    PWM reduces or eliminates dimming completely, so nearly all power goes to lighting.
    PWM fools the eye into thinking it is steady light and can dim it easily just by keeping it off more often

  20. #20

    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by xpitxbullx View Post
    Turn off your bathroom lights and close the door. Turn on your flashlight and run the shower. If the water looks like a flickering string of beads, then your flashlight is using PWM. If its just a blur of water then it's current controlled.

    Noticed that when my bathroom light went out and I had to shower by flashlight.

    Jeff
    Here's another way:

    For those of you with electric fans or something similar, go to your light's lower modes, you will see the blades moving erratically. If you work in situations with moving stuff like that then your lights does that, you WILL get a headache after a while. Which is why i stay away from lights with PWM, can't use 'em at work.

  21. #21

    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by pjandyho View Post
    Whilst I am sure you are right about the consistent color part, how does PWM equates to longer battery life? I am afraid I am clueless when it comes to this. Could you please enlighten me a little? Thanks!
    Yeah, i'd like to be enlightened by that factoid.

  22. #22

    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by shelm View Post
    The regular Quarks are current controlled, not PWM controlled, am i right/wrong?
    correct, Quarks are current controlled, but not all of them have voltage cut offs, Quark Turbo X is such an example, it will drain your rechargeable batteries to zero (0v) voltage, rendering them useless as chargers will not charge zero voltage cells. My older Quark AA^2 is much kinder to rechargeable cells because it would turn off when the voltage is not sufficient to sustain the light but not drain it to zero even if you left the light on overnight. (it's happened before, forgot the light, found it dead the next day, battery still had voltage, good light!!)

  23. #23

    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by Cataract View Post
    I can't remember for the life of me if it is the regular/tactical quarks or just the mini's or both. I'll have to check again when it's dark, because they use such high frequency PWM that it is very very hard to detect
    my quarks are both current controlled. did they release lights with PWM?

  24. #24

    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by 127.0.0.1 View Post
    circuits that provide steady power to the led must resist some of that power to in order to dim it,
    this creates some heat in the resistance circuit and eats power that otherwise could go to producing light

    PWM reduces or eliminates dimming completely, so nearly all power goes to lighting.
    PWM fools the eye into thinking it is steady light and can dim it easily just by keeping it off more often
    hmm, but wouldn't current regulated lights be more efficient as it is not resisting the power of the battery, but regulating it so a fixed amount of power goes to the emitter for the desired lighting level? making the led rapidly oscillating on and off (pwm) wouldn't that eventually shorten the life of the led?

    hmm, time to study the internals of our lights!

  25. #25

    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by subwoofer View Post
    A light whining is not an indication of PMW, it is the driver circuit boosting voltage.

    PWM is where the light output is flashing in order to achieve a higher perceived brightness for a lower power output, or by cheaper lights often to achieve the lower levels rather than using proper current control.
    Correct! The Quark buzzes when it's trying to regulate the output of the light when the cell is almost depleted. At first i thought my Quark was busted! Now I know that when it starts to buzz, i should be careful coz my light's running outta juice.

  26. #26

    Default Re: How to tell if your flashlight uses PWM or not

    I asked marshall about the PWM, and he said its not that noticeable so I guess I will try this XT11. I just love the Klarus interface! Tactical lights rock! (Provided the Strobe and Flashy modes are conveniently hidden) Never know when you need to strobe an attacker (animal or human) in the eyes while out at night!

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    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by roadkill1109 View Post
    hmm, but wouldn't current regulated lights be more efficient as it is not resisting the power of the battery, but regulating it so a fixed amount of power goes to the emitter for the desired lighting level? making the led rapidly oscillating on and off (pwm) wouldn't that eventually shorten the life of the led?

    hmm, time to study the internals of our lights!
    it depends on how much money you put into the circuit and driver. PWM is cheap and reliable and allows near infinite control, and of
    course easy strobe modes. I am going to back off on the efficiency part. there are many analog circuits driving LED that are more efficient than
    PWM...so my factiod isn't really a 'blanket statement'

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    Default Re: How to tell if your flashlight uses PWM or not


    From flashlight-wiki:

    PWM
    Pulse Width Modulation. A technique of varying the brightness of a LED by flashing it on and off very quickly, making it appear to the eye that the LED is dimmer. Good PWM is at such a high rate that you can't notice it. But if you wave your hand in front of the light and get a strobe effect, the PWM is getting too low. Some use current regulation which makes the light dimmer without PWM and is also more efficient.

    http://flashlight-wiki.com/Terminology#P

  29. #29

    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by 127.0.0.1 View Post
    I am going to back off on the efficiency part. there are many analog circuits driving LED that are more efficient than
    PWM...so my factiod isn't really a 'blanket statement'
    Correct - a true "current controlled" light does not use resistors to dump excess current as heat. The current-controlled circuits I have constructed use a mosfet, a transistor and a couple sense resistors (which serve only to "tune" the output current).

    A proper current controlled light will run much longer than a PWM-controlled one at the same output level - the difference can be upwards of 25%.

    http://www.molalla.net/members/leeper/pwm_cc.htm

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    Default Re: How to tell if your flashlight uses PWM or not

    Quote Originally Posted by 127.0.0.1 View Post
    circuits that provide steady power to the led must resist some of that power to in order to dim it,
    this creates some heat in the resistance circuit and eats power that otherwise could go to producing light

    PWM reduces or eliminates dimming completely, so nearly all power goes to lighting.
    PWM fools the eye into thinking it is steady light and can dim it easily just by keeping it off more often
    Thanks. I figured it was so but I just wanted your confirmation.
    The love of light is the reason why I don't walk in darkness. But darkness has it's beauty...Sadly, my lights are much more beautiful!!
    Beam shots Night Trekking with HDS high CRI and McGizmo Haiku & Mule high CRI

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