Why is PWM so Undesirable?

[kreisl]

i will prefer efficiency to pwm.

maratac AAA Rev3 is the most efficient nimh aaa light i know of. more efficient than any Worm, Tool, or other Maratacs, on matter if with pwm or without pwm or whichever revision.

so i accept it on this particular model revision.

on Max mode, one cannot see PWM anyway.

 

[chillinn]

i will prefer efficiency to pwm.

maratac AAA Rev3 is the most efficient nimh aaa light i know of. more efficient than any Worm, Tool, or other Maratacs, on matter if with pwm or without pwm or whichever revision.

so i accept it on this particular model revision.

on Max mode, one cannot see PWM anyway.

I suspect you can't see PWM on max mode because the Rev.3 is direct drive in max mode. But whether pwm can be seen or not doesn't make any difference. Lots of things that can't be seen can be harmful. Some PWM I can not see, but still messes with me. Whatever Zebralight is using in some modes, the not-quite-PWM pulsing scheme, causes me to want to fall asleep with heavy eyelids within 20 minutes. But even fast 17.5k PWM can trigger a headache after a while.

 

[ssanasisredna]

No, it can't trigger a headache at that PWM rate. That is just conjecture with no basis in verified study or the biology that could even cause an issue. The speed of chemical and neural response to light is well understood. We know fairly well where PWM is not an issue. What we don't know exactly is where it becomes a serious issue but it varies from 100% modulation at 1khz, to as little as 10-20% modulation at 100Hz.

Viewing things that are moving in a modulated manner I.e. a rotating fan, moving a light across a grate, etc will modulate PWM to a lower and visible frequency, but those are short term effects not the type that induces headaches.

Where people get headaches is also not so much from casual viewing, ie just sitting around a room, but from doing fine work, especially reading. Its primary cause is eye strain from sacchades over and undershooting causing subtle blurring and making your eyes work harder.

On movies, at least film, 24 images are taken per second but each image is flashed 3 times.

Technically there are good reasons for PWM including cost, size and efficiency implemented properly. In commercial lighting it is becoming more common and there is a good chance many reading this are sitting under fixtures that use PWM for brightness control.

 

[Bugdozer]

I read on another post that the NiteCore EC11 uses PWM so I shook mine violently and sure enough, the three mid levels use PWM. Low and High don't. Did I notice anything before then? Nope.

 

[jon_slider]

No, it can't trigger a headache at that PWM rate.

well, that is just rude
he just shared his experience from using Pulsed lighting
why call him a liar?

I suggest you not reply to individual posters who post their opinions, instead, reply to the original topic, with your own original thoughts

I hate to see this thread turn into yet another series of adhominem attacks, please attack the topic, not the poster
and I will try to do the same

 

[eh4]

PWM is neat for looking at water dripping, fans turning (but don't touch that "stationary" saw blade!).
It's neat in its own right but not for regular use.
What's much worse for me than PWM in a hand held light, is all of the PWM string lighting out there, move your head or shift your eyes too fast and it creates a disconcerting sense of discontinuity, like a micro seizure, or black out, or something. I despise PWM in area lighting, PWM car signal lights are almost as bad.

 

[ssanasisredna]

well, that is just rude
he just shared his experience from using Pulsed lighting
why call him a liar?

I suggest you not reply to individual posters who post their opinions, instead, reply to the original topic, with your own original thoughts

I hate to see this thread turn into yet another series of adhominem attacks, please attack the topic, not the poster
and I will try to do the same

I have no doubt that the poster believes a light PMWing at 17.5KHz is giving him a headache. In a similar fashion, I have absolutely no doubt that it is not. The poster did not share his experience that 17.5KHz PWM causes his headache, he posted that he believes 17.5KHz PWM causes his headache. It is not a subtle difference. I could post that I believed the world was flat based on my personal observations. I would be wrong and my post would be of no value and should be pointed out as inaccurate.

The poster is posting his opinion. I am posting a large body of scientific research that extends beyond just one person.

I am not attacking the poster, I am attacking the post. 17.5Khz PWM does not give you a headache. Period.


The thread is about why PWM is so undesirable. Posting a "feeling" that is not proven or factually accurate based on a wide body of information does not add to the subject and in fact detracts from it. To that end, it should be called out as inaccurate.

 

[ssanasisredna]

PWM car signal lights are almost as bad.

Specifically the tail running lights where the tail light is also the brake. PWM is used for the dimmer level. When that method first came out, ~200Hz was pretty common for the PWM. Last one I measured was several KHz.

 

[jon_slider]

it should be called out as inaccurate.

I understand that you have reason to believe that
instead of acting like the post police, I suggest you make a substantive contribution to the original question
"why is PWM so undesireable"

I for example, find it undesireable because it interferes with my photos, and I have no doubt it has more subtle effects that the canary in the gold mine can detect, but science does not address

glad we can be reasonable, as I dont mean to judge your knowledge, you clearly have a lot to contribute. I would like to learn more about things you know, without beating up on posters who "feel", unscientifically, uncomfortable with PWM for many reasons mentioned so far.. headaches is only one of them.

I will also now remove my own Post Police Hat
whirled peas.. the medium is the message

 

[nbp]

Ssanasisredna: it may help your case if you cite some articles in scientific journals regarding the PWM/headaches concern since it sounds like you have read some. As a biology nerd I would be very interested to read them too!

 

[ronniepudding]

Specifically the tail running lights where the tail light is also the brake. PWM is used for the dimmer level. When that method first came out, ~200Hz was pretty common for the PWM. Last one I measured was several KHz.

I'm glad to hear that they're improving by using faster PWM, but I wouldn't be surprised to learn that there are a significant number of vehicles with ~200Hz tail lights still on the road today.

 

[this_is_nascar]

Oh well. Probably time to unsubscribe from this thread.

 

[ssanasisredna]

Ssanasisredna: it may help your case if you cite some articles in scientific journals regarding the PWM/headaches concern since it sounds like you have read some. As a biology nerd I would be very interested to read them too!

Will see what I can link to that is not behind a pay wall. Some of stuff from the 80's, early 90's should be public domain by now.

 

[ssanasisredna]

I'm glad to hear that they're improving by using faster PWM, but I wouldn't be surprised to learn that there are a significant number of vehicles with ~200Hz tail lights still on the road today.

Tons. Virgil the moderator on the Automotive Lighting section can likely give a better answer. I am not sure how deep he goes on tail lights though. Keeping the frequency low is all a matter of EMI. Switching fast is easy and cheap. Doing it in the automotive realm with protection for shorts, EMI control, etc. adds cost ... which no one wants to pay for.

 

[nbp]

If it is well documented science, there should be plenty of well researched articles on it available.

 

[Launch Mini]

I had JW Speaker LED lights on my Jeep Wrangler. For some unkown (to me reason), Jeep uses PWM in their stock incan Headlights.
So with the JWS LED's they were really bright, and I never noticed the PWM effect while driving in rain or snow, BUT, when taking photo's of my jeep form the front, it created some really odd effects.
I don't mind PWM in my lights at all.

 

[gunga]

I'm quite surprised by the low frequency pwm found in LED bulbs for household use. I finally found a nicely tinted, dimmable G9 bulb, but the low frequency pwm is quite irritating. I also have a couple ceiling fixtures they also rely on this. Ugh.

I have several dozen philips LED pot light bulbs. They may rely on pwm but I have not noticed.

I think my general threshold is 5-6KHz. I rarely notice anything above that. The ReyLight ti lan uses 9KHz and I never detect any pwm unless I put a concerted effort into it.

 

[nbp]

Personally I can't detect PWM in any of my lights that have it, so to be honest, I don't care that much one way or the other if it's there. Unless someone who cares and can see it tells me it's there, I won't even know if it is or isn't. Even in use I have never noticed it with regard to moving objects. Who knows... PWM, no PWM, don't care.

 

[staticx57]

I had JW Speaker LED lights on my Jeep Wrangler. For some unkown (to me reason), Jeep uses PWM in their stock incan Headlights.
So with the JWS LED's they were really bright, and I never noticed the PWM effect while driving in rain or snow, BUT, when taking photo's of my jeep form the front, it created some really odd effects.
I don't mind PWM in my lights at all.

What are the chances your Jeep does not have PWM but rather is fed unsmoothed DC from the alternator?

 

[LeanBurn]

Frankly I don't care what ssanasisredna comes up with for his argument. He isn't me, what matters is my perspective on the topic as my dollar buys what I like.

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