Quick detection of pulse modulation in LED emitters.

[DaveTheDude]

Today I discovered that many cell phone cameras are excellent at detecting pulse modulation in LED emitters. (Apologies in advance if this is already widely known, but it's new to me, and I felt it to be worth sharing.)

Turn on the phone's camera, then point the light's beam just outside the image frame (placing the hotspot outside the image frame guards against false readings). Any PWM will show up as clearly visible pulsing of the camera image.

Give it a try.

 

[Duster1671]

That is a neat trick. However, if PWM is an issue in a particular flashlight then I'll know from using it. It's not a problem I want to go looking for.

 

[vicv]

Exactly. If you need a camera to find it who cares. Also that's more dependent of the cameras frame rate. It can pick up fluorescent and led house lighting as well

 

[thermal guy]

If you can't see it in normal use and eveverything looks good is there a reason to use other methods to detect it?

 

[Lynx_Arc]

What I wonder is if PWM that is undetectable in a light is a design advantage over the alternative. Can it make a light a little cheaper, have better range of modes, more efficient with power, and maybe other features?
I'm with most here if the PWM is not detectable then it shouldn't be an issue.
I think one other advantage with PWM may be tint shift that happens with voltage drop as the battery is depleted on some lights.

 

[PhotonWrangler]

What I wonder is if PWM that is undetectable in a light is a design advantage over the alternative. Can it make a light a little cheaper, have better range of modes, more efficient with power, and maybe other features?
I'm with most here if the PWM is not detectable then it shouldn't be an issue.
I think one other advantage with PWM may be tint shift that happens with voltage drop as the battery is depleted on some lights.

PWM is really annoying when it's too slow. Some brake lights use a too-slow PWM frequency and create a distracting flicker.

 

[xxo]

I can spot PWM on my camera and also on a fan (makes the blades look like they are slowing down), I can also see it on youtube vids on the lower modes.

I don't like PWM and usually try to avoid lights that are still using it.

 

[aznsx]

...more efficient with power...

I strongly suspect this might be the case, but have no test data, etc. to confirm that. If so, then this would obviously suggest impact on 'run time' using a given power supply, and that's something most would / should be interested in. Wish I had the time & test gear handy to investigate, but perhaps others may have numbers.

 

[KITROBASKIN]

Really slow pulse width modulation (like a Photon Freedom) will mess you up when using it in snowy conditions as well as some rain events. Very distracting, trance inducing.

 

[kerneldrop]

What brands or specific lights do not use PWM?

 

[Dave_H]

Simple way to detect PWM is to wiggle your fingers in front of it and count the multiples of four fingers; a sort of stroboscopic effect.

Another method which works with LED Christmas lights is to move the light rapidly back and forth. If the LED is being pulsed you should see gaps in the light bands, otherwise solid. You can get a good idea of duty cycle by the relative widths (for line-powered Christmas lights it is somewhat less than 50%).

Dave