# Do any lights not use PWM?



## sadbuttrue (Sep 9, 2013)

For those that don't know, PWM is a method used to dim LED lights by flashing them on and off many times a second. A longer off period results in a dimmer light and vice versa. The flicker is fast enough that human eyes do not see it. However, it can still lead to nausea, headaches, tired and painful eyes in a signfiicant number of people. Most bike lights when used below maximum brightness will employ PWM at a low enough frequency to cause issues. If you get home after a night ride and have eye related pain, chances are PWM was to blame.

Are any manufacturers of high powered lights producing PWM free options or looking into the possibility? The monitor industry finally recognised they could cash in on healthier monitors by charging a premium for their "flicker-free" options. Maybe bike light companies could do the same.


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## Cat-man-do (May 16, 2004)

My thoughts and opinion on this; Most of what you are saying is urban myth. PWM ( Pulse width modulation ) is used in a lot of common electronic applications. When functioning correctly the "duty cycle " of the pause, when used with lighting, is not perceivable to the viewer.

If the circuit ( or voltage source ) is not operating as designed it might be possible to see a slight flicker. Personally the only time I've ever seen this happen was with one of my cheap LED drop-ins. ( sometimes you get a bad one ) I've also seen this ( more commonly ) with fluorescent lighting when the bulbs get old or the ballast is malfunctioning.

Most people will not get headaches or nausea using devices that incorporate PWM circuitry. If that were not true no one would watch T.V. which still operate on line frequency that is only 60 Hz.

This said some people do have problems using computer terminals or watching T.V. for long periods. It really has nothing to do with PWM per say but instead is just a vision issue. By "Vision issue" I mean that some people have visual acuity issues that cause them problems. Some people can't drive at night because the high contrast between light sources gives them problems and yes some people get headaches and such. Working with something very close can cause the same issues. If you have problems seeing you can very easily get headaches but it has nothing to do with typical electronic devices that are functioning as designed and are adjusted properly by the user.

Yes, if you stare at a bright light ( PWM or no PWM ) long enough it will give you a headache. If you stare at a dimly lit book long enough that too can give you a headache. Has nothing to do with the light source, it has to do with how your eyes and brain work together. Some people genetically have better visual acuity, some have lousy visual acuity. All things are not equal. ( *note, there are hundreds of other things that can give you a headache as well )

Staring at a strobing/blinking ( low frequency ) light that is bright enough for a long enough period of time will of course make one ill. Then again only an idiot stares at a strobing lamp for more that a couple seconds.


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## 127.0.0.1 (Nov 19, 2013)

pwm can suck when done ultra cheap. most modern monitors today, even bottom barrel wallyworld ones, don't have the same issues as monitors 10 years ago. 

bike lights though ? 

cheap, high power LED lights commonly use pwm as it is accurate and cheap to build, vs current regulated which costs more. many people hate pwm leds, especially poorly timed ones. on the trail a bad pwm (skyray king style) can make you dizzy as f**k. handlebar and head bounce will bring out the strobe effect, and if you are on a section of babyheads and have crappy pwm...good luck with that. I will only use my skyray at 2000 lumens, at 300 lumens the pwm is so bad and noticable I want to scream. thankfully all my bike headlights that use pwm are very fast at the lumen levels I run, and I also have current regulated lights...I will not ride with bad pwm. 

I will not ride in snow or rain with any pwm if I can help it. serious visual b*lls**t with pwm in snow and rain


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## sadbuttrue (Sep 9, 2013)

The issue of PWM is real and well documented on various sites, from computer monitors to car headlights. A significant minority within the entire visual range are affected. Simply sit in a room with a PWM light pointed at the wall to your side and your preipheral vision will be enough to present symptoms. The brightness or visible flicker has no bearing.

As for rain issues I was having a space invaders moment the other day with my headmounted SolarStorm X2 on medium (forgot to set high). The rain falling in front turns into bright white long reflective strips - very disorientating.


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## JohnJ80 (Oct 10, 2008)

It's all about frequency. At about 60hz people can *maybe* detect it. Above that you are starting to switch faster than the rods and cones in your eyes can follow to where it is undetectable above about 100-200hz. If that is the case, there is no way for you to detect that there is any switching going on at all.

A lot of the power circuits in use today are switching at very high frequencies (as compared to 60Hz) for the simple reason that the capacitors and inductors get smaller and that means you can make the product physically smaller and cheaper. It also gets more efficient. It's common to have switching frequencies higher than 1Khz and up to 50Khz or even more.

So a lot of this invented as a problem. If the speed of the switcher exceeds the "frequency response" of the human eye by a large amount, it's going to be undetectable (and is).

I have a pretty good eye for this after having worked on video monitors back in the <60Hz days. For any of the good quality bike lights I have, it's completely undetectable. Most of the PWM LED driver chips take this all into account now and they are cheap.

J.


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## Cat-man-do (May 16, 2004)

127.0.0.1 said:


> ....cheap, high power LED lights commonly use pwm as it is accurate and cheap to build, vs current regulated which costs more. many people hate pwm leds, especially poorly timed ones. on the trail a bad pwm (skyray king style) can make you dizzy as f**k. handlebar and head bounce will bring out the strobe effect, and if you are on a section of babyheads and have crappy pwm...good luck with that. I will only use my skyray at 2000 lumens, at 300 lumens the pwm is so bad and noticable I want to scream. thankfully all my bike headlights that use pwm are very fast at the lumen levels I run, and I also have current regulated lights...I will not ride with bad pwm....


There are a lot of technical issues with how LED drivers are built ( or can be built ). Too many types to address all the issues. I suggest reading this thread over on CPF and pay strict attention to what SemiMan has to say.

I own about 10 high power LED torches that have multiple modes. I also own maybe 10 or so ( sorry I lose count ) high powered LED bike lights. None of those lights have any issues whatsoever with noticeable flicker due to PWM circuitry. Like I mentioned before I only had one LED drop-in that had some flicker momentarily but that might have been caused by a poor connection to the battery.

Riding over rough terrain at night can be disorienting, period. Even more so when you aren't using enough light. Add a poor mounting solution to that mix where the lamp is jiggling around and that isn't going to help. More light in technical situations is always the best way to go. I'm not saying that nothing is wrong with your Skyray lamp. If you can see flicker in any of the modes with the lamp not moving and the battery fully charged then something is wrong with the lamp. Either there is a poor connection ( somewhere ) with the lamp or a component on the driver/PWM circuit is not functioning as it should.

Another factor that doesn't get mentioned as much that can cause disorientation at night is "beam tint". The "Bluish" tints cause me problems. I prefer basic bright white ( 6000-6500K range ) or neutral white ( 5000-5500K range ) which in my opinion works best during the dry summer season. Neutral white is easy on the eyes. Some people only like the warmer tinted LED's.



sadbuttrue said:


> The issue of PWM is real and well documented on various sites, from computer monitors to car headlights. A significant minority within the entire visual range are affected. Simply sit in a room with a PWM light pointed at the wall to your side and your preipheral vision will be enough to present symptoms. The brightness or visible flicker has no bearing.


Not everything on the internet is going to be true. Visual acuity is likely the issue you are dealing with UNLESS you actually do have a bad lamp. Anyway, I suggest you watch a couple episodes of the TV series, "Brain Games". It is amazing how the brain can play tricks on, "What you think you see and what's really there".


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## zen bicycle (Mar 23, 2007)

We do not use PWM in any of our lights to answer your question. And maintain a color temperature between 5500 and 6000k

Thanks


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## 127.0.0.1 (Nov 19, 2013)

Cat-man-do said:


> I own about 10 high power LED torches that have multiple modes. I also own maybe 10 or so ( sorry I lose count ) high powered LED bike lights.


ummm, I know a bit about lights

I have >84 lights, mostly high power LED. from a few 4sevens to several (8) Veleno Designs and everything in between. One of my McGizmo Haiku's is high-cri XML with a Flucero 5-speed driver. I know what crap light is and I know what good light is.


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## pimpbot (Dec 31, 2003)

sadbuttrue said:


> .... with my headmounted *SolarStorm X2* on medium (forgot to set high).....


Well, here's your problem. The issue is not that your light uses PWM, it's that your cheapo light uses crappy, slow rate PWM.

I ride at all the time with my NiteRider Minewt Dual 700, and I can't see the PWM... and I ride on low or medium the majority of the time. I see the same issues you're seeing with my old Magicshine, tho.

BTW, thanks for talking me out of buying a SolarStormX2. You just saved me dozens of dollars.


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## sadbuttrue (Sep 9, 2013)

I cannot see the PWM even on low with the SolarStorm, which is the point I've been trying to make. Anything above ~120hz with a decent duty cycle will not be visible to the naked eye. The rate needs to be in the khz range and above to prevent eye fatigue for a good number of people. An expensive light does not guarantee this, since no company publishes figures* and no-one has yet bothered to run tests. Another side effect of PWM is interference with wireless signals, such as a cycle computer. 

I'll try to measure The Solarstorm rate when I get a chance.

*Trail LED confirming above they are PWM free.


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## manbeer (Oct 14, 2009)

Very interesting, a few years ago after buying magicshines (had been out of the riding scene since the halogen days) i was riding and noticed a strobe like effect on my tire at certain speeds that almost made it look like it was stopping and rolling in reverse. Now it makes sense!


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## 127.0.0.1 (Nov 19, 2013)

even worse is if you can hear the pwm. really bottom barrel drivers emit a whine that may be heard at low light levels. the driver might be rock solid and never fail, but it is the execution (circuit design) that makes a big diff.


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## longhaulcommuter (Jan 3, 2014)

That explains why I can see the things like rain drops stop moving momentarily on rainy days or things flicked up by the tire when I am using my alternate headlight, a Costco 250 lumen flashlight. But only on low setting. On high setting, I don't see them.


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## GooglieS (Nov 16, 2008)

Do we have a list of PWM-free bike lights? Trailled costs like a steel bridge..


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## -Archie- (Aug 25, 2013)

JohnJ80 said:


> It's all about frequency.


Exactly, and in addition - the duty cycle of pulses: at the max output level, it's not detectable anyway.

Al reduced power, the only issue of PWM is a strobe effect, noticeable on moving spokes/tyre, rain drops etc.

Funny enough, sometimes cheap bike light have higher frequency of driver than relatively expensive one...


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## scar (Jun 2, 2005)

GooglieS said:


> Do we have a list of PWM-free bike lights? Trailled costs like a steel bridge..


My Amoeba lights do not PWM. Shoot me an email to my address in my signature :thumbsup:

*****


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## tigris99 (Aug 26, 2012)

Scars lights I think are one of the elite few that doesn't use pwm. 
Pwm isn't a bad thing if done right. Too low of frequency can cause a headache in sensitive people. But trying to say its some big deal that causes health problems is a bad joke. The visual effects of pwm your exposed to daily. Cars with chrome wheels, traffic passing cross ways at night, old version tvs/computer monitors and the list can go on.


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## Vancbiker (May 25, 2005)

tigris99 said:


> Scars lights I think are one of the elite few that doesn't use pwm.


That's because Scar uses the best of drivers, Taskled.


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## -Archie- (Aug 25, 2013)

tigris99 said:


> Pwm isn't a bad thing if done right. Too low of frequency can cause a headache in sensitive people.


Is there any exact data? I mean scientific articles with frequencies, duty cycles etc, not urban legends. The only issue with strobe effect I'm aware of, is that it's dangerous in case of epilepsy...



> But trying to say its some big deal that causes health problems is a bad joke. The visual effects of pwm your exposed to daily. Cars with chrome wheels, traffic passing cross ways at night, old version tvs/computer monitors and the list can go on.


Sure.


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## tigris99 (Aug 26, 2012)

Its not dangerous, but strobe effect can give headaches just from your eyes constantly trying to adjust. Not a health concern but go stare at a bright flashing light, after a little bit you can get a mild headache just from eyes being strained. Beyond that the only risk is as you said, epilepsy. Those with it it can cause an episode.


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## -Archie- (Aug 25, 2013)

tigris99 said:


> Its not dangerous, but strobe effect can give headaches just from your eyes constantly trying to adjust. Not a health concern but go stare at a bright flashing light, after a little bit you can get a mild headache just from eyes being strained.


Maybe some light power & frequency can do that, but till now I've never encountered such effect. At least, watching TV or reading under fluorescent lightbulb certainly doesn't affect me nor any people I know - hence my question about any scientific/medical data about "undesirable" frequency.

I'd like to compare that data (if any) to the working PWM frequency of several bike lights I have...


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## GooglieS (Nov 16, 2008)

Finally I got my cateye volt 800. I can't see any flickering on all modes. Great! But the beam is pretty narrow and has a square shape. Great for commuting but not good for trails or mountains. 

Отправлено с моего HTC Desire EYE через Tapatalk


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## GooglieS (Nov 16, 2008)

It looks like this. Camera was on a manual mode. I tried to represent the actual brightness.










Отправлено с моего HTC Desire EYE через Tapatalk


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## Ofroad'bent (Jul 10, 2010)

I have a KD 10 step driver in my Yinding. On low settings snowflakes and raindrops turn into dashed lines- you can definitely see the pwm. I only use this level for hiking, trailside bike adjustments and repairs, in transition at races etc.


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