How to tell if your flashlight uses PWM or not

xpitxbullx

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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
 

ragweed

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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.
 

subwoofer

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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.
 

subwoofer

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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.
 

subwoofer

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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
 
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calipsoii

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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.
 

pjandyho

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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.
 

Cataract

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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...t-is-it-How-does-it-work-and-how-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.
 

127.0.0.1

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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.
 

pjandyho

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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!
 

jorn

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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.
 

Cataract

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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
 

127.0.0.1

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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
 

roadkill1109

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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.
 
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