PWM and Eye Strain

I'm one of those people that doesn't care for PWM, both for efficiency and aesthetic reasons. Recently I've noticed that it's more difficult to see things at night when I'm using the High 2 level on my Zebralight H51Fw vs. Medium 1, which is dimmer but current-regulated. Something about PWM is fatiguing to my eyes and brain, and is subtly disruptive of depth perception. It reminds me of the eye strain one gets when staring at a computer monitor for too long, especially the old CRT screens.

Has anybody else noticed anything like this with PWM lights?

I think this topic has been covered pretty extensively here on CPF.
Some people don't think it's a big deal and I think others probably make more of a fuss over it than it deserves. I will admit that I do consider myself PWM adverse but when it comes to Zebralights I think the frequency is so high it's really hard if not impossible to tell. I once owned a Coleman Xponent headlamp that had such a low frequency PWM, I think it was probably 40-50 Hz, it drove me completely nuts - I had to get rid of it. But the ZLs are different I think, correct me if I'm wrong, the frequency is 120+ Hz so perhaps there's a little mental priming involved here. Did you know that the lower sublevels were PWM controlled before you used the light or after because I think it would be impossible to tell with the naked eye - you would need some kind of detection device.

Imon said:

... but when it comes to Zebralights I think the frequency is so high it's really hard if not impossible to tell. ... I think it would be impossible to tell with the naked eye - you would need some kind of detection device.

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I'm not sure about the ZLs high PWM, but I use moonlight a lot (on a H51w) and that PWM's frequency is really slow - can easily see it waving my hand in front of it.

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You couldn't give me a light with noticeable PWM.

or

I wouldn't even give away a light with noticeable PWM.


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I've still got my first L0D which has very noticeable PWM on the lowest level, but just like other light sources that are less than optimal, I can still use it and not notice any eye strain. Mostly just annoying when it's raining/snowing or working with running water.

Newer PWM lights are generally coming with a high enough frequency as to be undetectable, but unfortunately the problem hadn't been properly addressed until just a couple years ago.

For me at least, over ~ 800 hz or so, it is a non-issue.

In field use, I don't have a problem with it...and being ABLE to see the effect with a contrasting out of phase source, etc...is not a practical concern. If the effect is so slow it might as well be a strobe light, well, yeah, that's distracting. If all it does is make the light run longer/cooler...and I'm not noticing it, sweet.

A candle that flickers doesn't bother me. The 60 hz refresh rate on the tv screen doesn't bother me...but I CAN see it if I move my hand in front of the tv, etc. The flickering florescent lights at the big box store doesn't bother me, etc....but the buzzing noises do.

Imon said:

I think this topic has been covered pretty extensively here on CPF.
Some people don't think it's a big deal and I think others probably make more of a fuss over it than it deserves.

Click to expand...

Not trying to beat a dead horse here, but I hadn't noticed anything specifically referencing the more subtle effects of PWM with respect to long-term use at night. It could be all in my head, that's why I'd like to know if other people have experienced something similar.

ZL PWM is pretty difficult on lower levels when reading. For instance, reading my kindle by H60W on lowest is unreadable due to the shaky PWM. The next level up isn't distractingly bright, but the lowest would be more comfortable for the wife when reading in bed.

PWM is okay in most applications, like looking for a bump in the night, but anything relating to movement, makes it very noticeable, and can make me rather sick. Reading, you are moving your eyes from word to word, and the words seem to move about too much. Walking, or riding, or running at night, and depth perception suffers, also gives me a bit of vertigo depending on the light. Again, the higher the frequency, the less it affects me, but surely you could use a resistor AND PWM to drop the brightness and maintain colour?

The PWM on some car rearlights (mainly Volvo's and Cadillacs) is actually dangerous for me.. it makes me see double, my eyes can't focus and want to shut.

On flashlights with higher frequency PWM, eye strain is somewhat reduced with use of a diffuser. Tried on older series LD01.