100Hz flicker in lighting is a problem?

[ocset]

Hello,
Please can we   de-nonsense   the  “100Hz flicker problem” in lighting?

The web is full of conflicting stories  about  whether or not  100Hz flicker is  actually harmful to humans.

I believe that 100Hz flicker in lighting is no problem whatsoever…..i lived under the old magnetic ballast fluorescent lighting for decades…and had no problem with its 100Hz flicker. Also, driving down motorways with sodium vapour lamp streetlighting which flickers at 100Hz,  caused me no problem whatsoever…..and no problem to other drivers either.

Headaches  in today’s world are more likely to be caused by Hangovers, too much caffeine, too much sugar, too little exercise, too little sleep due to watching Netflix all night, etc etc…..

The 100Hz flicker problem in lighting is simply a nonsense story pervaded by large  electronics corporations so that they can sell their integrated circuits and lamps  which get rid of this 100Hz flicker.
Also, most of the large electronics corporations have decided to volume manufacture LED power supplies with large-ish  electrolytic capacitor banks, (eg after the PFC stage) which makes them cheaper and easier to design……..and means the 100Hz flicker is easily avoided…….having committed their resources to this in vast quantity, they then are looking to create nonsense stories about smaller manufacturers who make lamps which do flicker at 100Hz….in  other words, yet again, all we are  seeing, is the large globalist corporations lobbying Governments so as to increase their profits and destroy their smaller rivals.

Surely you agree?

I mean, they are looking to make greedy mega bucks by replacing all  the old 100Hz flickering sodium streetlamps with their flicker free  LED offerings....but first, they have to pervade their nonsense  health hazard stories about 100Hz flicker.

There is not one single piece of conclusive evidence to state that 100Hz lighting flicker is actually a problem……..nonsense?

http://luxreview.com/article/2018/04/street-light-flicker-is-new-hazard-says-watchdog

3:43 to 4:43 of this video shows how the global corporastions lobby governments to favour their own profit making rackets, eg in the case of 100Hz flicker stories....

[Siwastaja]

Depends on the amplitude and shape (duty cycle) of the 100Hz! That's one of the reasons for so many conflicting views - there are so many levels of "flicker".

Also, people are really different. We do have physiological differences. Sensitivity to flicker is a classic discussion. Similarly, motion picture film projectors existed in two varieties, 48Hz and 72Hz flicker, and people had strong opinions on them.

For example, the traditional incandescent lamp flickers at 100Hz but the amplitude is only about 10-30% peak-to-peak of the full power. Fluorescent is more flickery, but the fluorescent material they use still has some "delay" in it. The amplitude of the flicker is not even near to 100%. Fluorescent lamps tend to also flicker in different colors; the spectrum varies as a function of time.

With LEDs, it depends a lot of the driver. For example, if you drive "raw" from full bridge rectified mains, with capacitive or resistive dropper, so that the Vf of the LEDs is fairly high, it means they conduct only a small portion of the cycle, giving a very strong flicker - amplitude is 100% and duty cycle may be as low as 30%. These kind of bulbs do exist and some people are fine with them, but some are not. Personally, I don't like them at all, I'd call them disastrous. When you move your hands quickly, you get the strobe effect.

People actually getting migraines or epilepsy is AFAIK not very common, but still a valid concern.

If at all possible, please design your LEDs to be fairly flicker-free. No need for perfectionism here, but I think solutions which only use a small portion of mains cycle without storing any energy are out of question.

I don't think there's a conspiracy out there. I have seen so many shitty, flickery lamps existing!

It's well possible that marketing exaggerates the flicker problem to sell products and lobby. That's how marketing works. But even if the problems of flicker were exaggerated by some, it's still a very good idea to limit it to sane levels.

[Twoflower]

One I was in a Hotel that had all lights converted to (cheap) LEDs. All light in the room flickered synchronous to each other and it was not very bright light. The result was moving in the room made feel me dizzy. While stay still was no problem. Except in the peripheral view. It took a few hours to get used to that. Nothing I would recommend to live in. I never experienced this with fluorescent light. Not even close to that, except with fast running stroboscope lights. In fact my desk lamp is still using a fluorescent tube with a old balun and I never had an issue with that having this as only light in my room (similar brightness like the said hotel room). Obviously LEDs can be driven in modes that this stroboscopic effect is very intense.

Please note that I seem to recognize reasonable high flicker frequencies but has no direct issues with such conditions.

Also working with machines can be dangerous under such conditions. As the stroboscopic effect might trick your assumption of the rotation speed. That's the reasons that in some countries are rules for fluorescent lights in machine halls need to be supplied from different phases or other measures to prevent the stroboscopic effect (e.g. Duoschaltung; sorry no english entry).

Edit: Added link to Duoschaltung

[mikerj]

Hello,
Please can we   de-nonsense   the  “100Hz flicker problem” in lighting?

The web is full of conflicting stories  about  whether or not  100Hz flicker is  actually harmful to humans.

I believe that 100Hz flicker in lighting is no problem whatsoever…..i lived under the old magnetic ballast fluorescent lighting for decades…and had no problem with its 100Hz flicker. Also, driving down motorways with sodium vapour lamp streetlighting which flickers at 100Hz,  caused me no problem whatsoever…..and no problem to other drivers either.

How do you know that no other drivers were affected by flicker?  Has every single driver been questioned?  Do you believe every single person has the same sensitivity to flicker?

[ocset]

Ive never met  anyone who was sensitive to flicker...i have never seen any of the effects of flicker that are described here...i am in my 40's.
How do you know that the "flickering" led lights were not suffering some feedback stability loop thing?

I can honestly say that lighting in a room, dim or not, has never ever made me dizzy...and i never met anyone who said this.

Ive been to loads of nightclubs where the lighting was deliberately flickering very fast ( i used to work in one like this)...and if you moved your hand across your face, it was kind of weird seeing it jagger across....but i did not mind at all...and none of the other 1000's in the packed nightclub left the club because of it.....you did not get lots of people leaving saying...wow...i just couldnt handle those flickering lights...had to go home early.

Also working with machines can be dangerous under such conditions. As the stroboscopic effect might trick your assumption of the rotation speed

Now this anyone would say is a good point...so for those particular places, yes....even then, people shouldnt be going anywhere near ungaurded electical machines that are rotating whatever the lighting

[Siwastaja]

Ive never met  anyone who was sensitive to flicker...

I knew one guy who was somewhat sensitive to mains frequency fluorescents (@ 100Hz)! And he was serious about it.

Now, the important takeaway is that a "flickerily" designed LED source can be an order of magnitude worse than a fluorescent. Haven't talked to him since LED lamps got more widespread, however...

i have never seen any of the effects of flicker that are described here...i am in my 40's.

The reason might be that you simply haven't seen the "worst offenders", or you just don't know anyone who's suffered from them.

The fact this doesn't seem to be a problem might be just because the designers know flicker is a problem and hence, design the products to be non-flickery!

How do you know that the "flickering" led lights were not suffering some feedback stability loop thing?

Well, that's a possibility, too. The reason of the flicker is irrelevant, but you need to limit the amount of flickering to manageable levels.

I can honestly say that lighting in a room, dim or not, has never ever made me dizzy...and i never met anyone who said this.

I agree it isn't common enough. Although, I have never known or heard of anyone being allergic to nuts directly... Yet it's a true fact that some people are deadly allergic to nuts - and it even isn't very uncommon!

It's just that your personal ring of people you discuss lighting details with is most likely very small.

Also, most people who get a headache from poor lighting would just leave the place and be done with it, and forget the incidence. It's an unfair expectation that they would know you are interested about this and come to you with this information!

Ive been to loads of nightclubs where the lighting was deliberately flickering very fast ( i used to work in one like this)...and if you moved your hand across your face, it was kind of weird seeing it jagger across....but i did not mind at all...and none of the other 1000's in the packed nightclub left the club because of it.....you did not get lots of people leaving saying...wow...i just couldnt handle those flickering lights...had to go home early.

Well, I think people do get a headache at nightclubs, and I think people do need to leave these places. I guess these places even employ staff to look at people not feeling well. They even tend to implement "closing hours" to limit the exposure times.

I guess countless people actually die due to visiting these places. People go there to deliberately poison themselves, anyway, and purposefully cause physical damage to themselves.

The flickering lights are supposed to make you feel dizzy, just like the alcohol they serve!

That's the whole idea.

Now, I'm very sure there are a lot of folks who don't go to nightclubs - for example, me. I would get a headache quite soon, probably as a combination of loud noises, and possibly flickering lights - even without any alcohol.

Note that the number of people who enjoy nightclubs and visit them without getting a headache is a very small minority. Most of the people just don't visit nightclubs too many times during their life, and most of those who do visit them are having a serious headache the next day. And I guess many don't want to try to classify the exact reasons for the headache. We all know what the number 1 is, but how about all the other contributing factors?

But I guess most people wouldn't like to have a nightclub at their home, 24/7. That could cause some serious headache.

[maukka]

Slow LED flicker is the worst. I don't get any symptoms like headache from it but in some situations it is very visible and annoying. Most people don't see or care about the usual 100/120Hz flicker, but playing with frequency, duty cycle and modulation depth everyone will see it with suitable parameters. With low duty cycle and true on/off PWM it can be seen up to several kHz if you know how to look for it with rapid eye movements.

Here's a good introduction and a single unit to evaluate flicker visibility: https://www.derlichtpeter.de/en/light-flicker/cfd/

Also in the flashlight world there's a huge variety of drivers for LEDs and some work has been done to estimate the visibility of flicker: http://budgetlightforum.com/node/57087

Just like with everything, YMMV. But just because it doesn't bother you, doesn't mean that others can't see it. Although I don't claim it has any effects on general health.

[ocset]

But just because it doesn't bother you, doesn't mean that others can't see it.

Thanks, there's never been a significant study done with unbiased groups of people being placed into rooms with/without flicker, and then seeing if they get headaches with /without the flicker being there.
This says it all........this is nonsense pervaded for reasons of financial gain, as described in the top post.

[Twoflower]

I think the LEDs actually had no driver real that could run havoc. One part of the lighting was a chandelier with several cheap filament replacements. They flicker synchronous to each other and with some single LEDs mounted in a wall. As all light sources are independent from each other I'm sure they're running synchronous at 100Hz. The interesting part is that I had the feeling that the 'see the world around me' wasn't the problem. The problem was the sense moving around didn't match to the visual.

Just one thing that just came back to my mind. Few moths ago I came to a customer office. And they replaced the T8 tubes in the ceiling with LED replacements. I noticed that flicker too, even with some additional daylight from windows. If I would work there I would actually do something to change that (e.g. LED with decent driver) as sitting under that light 8h+ a day would have an impact to my concentration. I have no problems working under fluorescent light and never noticed such things there. And fortunately so far for me that's only an annoyance.

One study for example (I just read the abstract) also note the list of references at the end. there are many studies listed with this specific topic:
https://www.ece.neu.edu/groups/power/lehman/Publications/Pub2010/2010_9_Wilkins.pdf
And you can find some more using your preferred search engine.

Note that I'm also 40+. This is a completely new effect to me to see this in lamps. I've noticed that in old computer screens 20something years back and I'm happy that this problem is gone with LCDs. Still under certain conditions I can see the OLED screen of my Samsung flicker too. But it seems that this now come back with cheap LED lamps. And potentially the microLED screens in future...

[maukka]

Some LCD monitors and especially televisions are notorious for having a PWM driven backlight, which flickers very clearly. At least TFT Central tests for this

[Siwastaja]

But just because it doesn't bother you, doesn't mean that others can't see it.

Thanks, there's never been a significant study done with unbiased groups of people being placed into rooms with/without flicker, and then seeing if they get headaches with /without the flicker being there.
This says it all........this is nonsense pervaded for reasons of financial gain, as described in the top post.

It seems you have already made your mind of rationalizing your shitty design - simply for your company's financial gains to save cost!

So why are you asking here when you already have your own "truth"?

Or were you just expecting confirmation to your rationalization, and now it backfired when people start telling their personal experience?

BTW, if you google for "lighting flicker study", you'll find a lot of scientific research about the matter. But it takes quite some time to go through enough material. Clearly, the flicker has been officially considered a health risk, hence standards exists. But you can, of course, decide that it's a further proof of a conspiracy, and a further confirmation for your rationalization - to allow you save money further in your shitty design and still feel good.

[bd139]

Treez: that youtube video is basically a load of bollocks run by a bunch of crackpot fucknuggets who's entire empire is run from being contrarian to rationality. Please stop watching stuff like this and getting angry. Develop some critical thinking skills.

This isn't about 100Hz flicker as such. It's about visual noise. If you have a 100Hz flickering LED light and 101Hz flickering TFT backlight for example then you get the thing beating at 1Hz resulting in some wierd visual artifacts. These are terribly difficult for the brain to process as it reacts quicker to contrast, which results in fatigue and at higher frequencies, actual fits. I know this having spent a good few years on anticonvulsants.

[rstofer]

In the early days of fluorescent lighting, the stroboscopic effect of flicker could make rotating saw blades appear to be switched off.  The ballast designers went to some effort to put a phase shift between the lamps to prevent this effect.

Ignoring all other physical issues, in terms of lighting only, I would be concerned that flicker might cause that stroboscopic effect to return.

https://www.electrotechnik.net/2015/11/stroboscopic-effect-in-fluorescent-lamps.html

[edavid]

If you have a 100Hz flickering LED light and 101Hz flickering TFT backlight for example then you get the thing beating at 1Hz resulting in some wierd visual artifacts.

No you don't, because there's no nonlinear element (mixer).  Two frequencies adding together in a linear element don't make a beat frequency.

[NiHaoMike]

Some LCD monitors and especially televisions are notorious for having a PWM driven backlight, which flickers very clearly.

That's often done intentionally to reduce motion blur, by transitioning the pixels while the backlight is off. LightBoost is one of the marketing names used.
https://www.blurbusters.com/zero-motion-blur/lightboost/
At 120Hz, the flicker is not noticeable.

[maukka]

Even though PWM is used in blur reduction technologies such as Lightboost or black frame insertion many normal non-gaming monitors suffer from it as well. And 120Hz PWM is very visible to some people even if it doesn't bother you.

[NiHaoMike]

Those who are bothered by 120Hz flicker must have had a really bad time back in the days of 60Hz TVs. There are also 240Hz monitors and TVs out there, but they're mostly for 3D glasses so that the effective framerate would be 120Hz after the glasses demultiplex it.

[maukka]

60Hz television would have been a luxury in a country with the 50Hz PAL system. But with practically no persistence, LEDs are much worse than a CRT screen at similar frequencies. 100Hz televisions/monitors seemed perfectly stable to me back then, but I haven't checked one out for quite a some time.

[ocset]

Also, all British motorways were, and often still are , lit with 10's of thousands of orange sodium lamp streetlights, which flicker at 100hz...and they go to zero current (zero light) every 10ms.........there has never been one single complaint from a driver about these streetlights....i think this says it all.

[bd139]

If you have a 100Hz flickering LED light and 101Hz flickering TFT backlight for example then you get the thing beating at 1Hz resulting in some wierd visual artifacts.

No you don't, because there's no nonlinear element (mixer).  Two frequencies adding together in a linear element don't make a beat frequency.

There are three very non linear elements in your head.

Watch this. I connected two cheap red LEDs to my FG and set them at 6Hz and 5Hz respectively 50% duty cycle. Note at approx 1Hz there is an intensity gradient.

I had to slow this down to 5/6Hz to maintain video quality as the camera is good for about 30fps only unlike the brain.  Average eyes and  brain and eyes can see this up to about 60Hz. 60-120Hz depends on the person.

https://youtu.be/TM6Y0cYLVU0

Edit: updated number of non linear elements to three because the brain has its own abstraction over what is going on.

[floobydust]

You have to consider the physiology of vision, the biomechanics.
It's very difficult to put in electrodes (in animals) to get the time constants out of a region of the brain that does the auto-focus and positioning for us.

As you read this, your eye is micro-focusing and moving from letter to letter.
An entire servo system, that does not like flicker lest it cause eye-fatigue from its muscles going back and forth. Or it simply fails to focus/position in time to avoid an accident due to a strobing streetlight.

Or perhaps there is a heterodyning issue, between two independent light sources.

[Marco]

Those who are bothered by 120Hz flicker must have had a really bad time back in the days of 60Hz TVs.

You don't have parallax planes moving independently while being lit by a stroboscopic light on a TV. Nor does the TV have a mix of continuous and stroboscopic lit movement from background light combining with the stroboscopic light.

60Hz television would have been a luxury in a country with the 50Hz PAL system. But with practically no persistence, LEDs are much worse than a CRT screen at similar frequencies.

Once you're above the flicker limit for displays, low persistence is far better for motion until you hit very high framerates (actual fully rendered framerates, not just screen updates). So if you can only generate say 100 fps, you want a low persistence display.

LED lit and OLED displays are almost always capture and hold, high persistence. Nice to display a photograph, not so much for moving images.

[james_s]

Harmful? Probably not directly, but it certainly is annoying.

Here HID, magnetic ballasted fluorescent and some LED lights flicker at 120Hz and that's bothersome to me, 100Hz is significantly worse. I suppose you get used to it but when I visited the UK the flicker was quite pronounced. I also noticed that motors and transformers sounded strange to me. You get used to a certain frequency of "electrical hum" and when it's suddenly different it really becomes noticeable. A friend of mine who lives over there has said the same thing when he's visiting the US, the refrigerators and air conditioners and such all sound weird to him.

[tooki]

Hello,
Please can we   de-nonsense   the  “100Hz flicker problem” in lighting?

The web is full of conflicting stories  about  whether or not  100Hz flicker is  actually harmful to humans.

I believe that 100Hz flicker in lighting is no problem whatsoever…..i lived under the old magnetic ballast fluorescent lighting for decades…and had no problem with its 100Hz flicker. Also, driving down motorways with sodium vapour lamp streetlighting which flickers at 100Hz,  caused me no problem whatsoever…..and no problem to other drivers either.

Headaches  in today’s world are more likely to be caused by Hangovers, too much caffeine, too much sugar, too little exercise, too little sleep due to watching Netflix all night, etc etc…..

The 100Hz flicker problem in lighting is simply a nonsense story pervaded by large  electronics corporations so that they can sell their integrated circuits and lamps  which get rid of this 100Hz flicker.
Also, most of the large electronics corporations have decided to volume manufacture LED power supplies with large-ish  electrolytic capacitor banks, (eg after the PFC stage) which makes them cheaper and easier to design……..and means the 100Hz flicker is easily avoided…….having committed their resources to this in vast quantity, they then are looking to create nonsense stories about smaller manufacturers who make lamps which do flicker at 100Hz….in  other words, yet again, all we are  seeing, is the large globalist corporations lobbying Governments so as to increase their profits and destroy their smaller rivals.

Surely you agree?

I mean, they are looking to make greedy mega bucks by replacing all  the old 100Hz flickering sodium streetlamps with their flicker free  LED offerings....but first, they have to pervade their nonsense  health hazard stories about 100Hz flicker.

There is not one single piece of conclusive evidence to state that 100Hz lighting flicker is actually a problem……..nonsense?

Wooooow… duuude. This is taking your ignorance to a whole 'nother level. How the f**k are you working as an engineer at a lighting manufacturer when you demonstrably know nothing about electronics or lighting?!? And even worse, seem hell-bent on not learning. You come here and basically ask for people to confirm your latest crackpot theory or design…

Is flicker harmful as in causing illness or injury? Not directly. But it does cause headaches in some people, and it is annoying to many more, and the strain of trying to ignore the flicker can be exhausting. And finally, flicker can be distracting (especially in peripheral vision), which can be dangerous.

Learn about the "flicker fusion threshold". Please. (Executive summary: to eliminate the chance of flicker in ALL situations, you need a PWM frequency of up to 30KHz.)


As for the conspiracy theory about manufacturers inventing a problem: oy gevalt… No. They don't need to invent reasons to avoid flicker, because enough people perceive flicker as annoying and distracting to complain about it.

[tooki]

Those who are bothered by 120Hz flicker must have had a really bad time back in the days of 60Hz TVs. There are also 240Hz monitors and TVs out there, but they're mostly for 3D glasses so that the effective framerate would be 120Hz after the glasses demultiplex it.

60Hz CRT TVs were OK for two reasons: phosphor persistence, and the fact that you look at a CRT straight-on. In peripheral vision, you might catch slight flicker.

120Hz LED is a totally different beast. It has zero persistence, so especially in peripheral vision, it's easily noticed, especially when your eyes, head, or the light source are in motion. You also should google the "flicker fusion threshold".

[james_s]

Yes, and also you aren't normally sitting very close to a CRT TV, computers on the other hand, 60Hz refresh on a larger SVGA monitor was horrid, some people didn't seem to notice at all but I couldn't stand it. Bump it up to 70-75Hz and it almost vanished to my eyes. On smaller monitors and those that displayed light text on a black background the flicker was not noticeable.

The first time I saw a PAL-50 TV I was blown away at how flickery it looked, it was almost like looking into a strobe light. I'm pretty sure it's one of those things where if you see it all the time you get used to it and your brain tunes out the flicker.

Personally I find that when I'm tired I'm much more sensitive to flicker. I have an older TDS scope with a sequential color display and normally it looks fine to me but if I try to use it when I'm very tired the flicker is pronounced and gives me a headache. I still love that display due to the novelty though, full color out of a B&W CRT with no shadow mask, it's neat, but that's off topic.

[NiHaoMike]

120Hz and 144Hz monitors that have pulsing backlights have selection of what duty cycle to pulse at. I run mine at 5% for the least motion blur. For general lighting, I see no reason to use such a low duty cycle. Or any real reason to use low frequency PWM dimming in the first place. Even cheap capacitive ballasted LEDs are not that difficult to get flicker free.

I like to know about the one who claims to be able to see flicker at 30kHz. In PC gaming, 144Hz is a popular choice for high end monitors and anything more is considered far into diminishing returns.

[tooki]

Yes, and also you aren't normally sitting very close to a CRT TV, computers on the other hand, 60Hz refresh on a larger SVGA monitor was horrid, some people didn't seem to notice at all but I couldn't stand it. Bump it up to 70-75Hz and it almost vanished to my eyes. On smaller monitors and those that displayed light text on a black background the flicker was not noticeable.

Yes!! I also assumed that the phosphor persistence on computer displays was shorter than on TVs, given the difference in effect.

The first time I saw a PAL-50 TV I was blown away at how flickery it looked, it was almost like looking into a strobe light. I'm pretty sure it's one of those things where if you see it all the time you get used to it and your brain tunes out the flicker.

Same here, as an American who moved to Europe! I found 50Hz TVs to be flickery even head-on. It's no wonder that 100Hz TVs were common in Europe if you could afford one, whereas I'm not even sure if 120Hz TVs were ever made.

Personally I find that when I'm tired I'm much more sensitive to flicker. I have an older TDS scope with a sequential color display and normally it looks fine to me but if I try to use it when I'm very tired the flicker is pronounced and gives me a headache. I still love that display due to the novelty though, full color out of a B&W CRT with no shadow mask, it's neat, but that's off topic.

Any info you can share on this??

I like to know about the one who claims to be able to see flicker at 30kHz. In PC gaming, 144Hz is a popular choice for high end monitors and anything more is considered far into diminishing returns.

You don't need it for a display, but that's not the topic of this thread. Again, google the "flicker fusion threshold" to learn about low duty cycle and saccading. Until you have, don't dismiss flicker even at high frequency.

[Tomorokoshi]

I like to know about the one who claims to be able to see flicker at 30kHz. In PC gaming, 144Hz is a popular choice for high end monitors and anything more is considered far into diminishing returns.

Let't calculate.

You sweep your eyes at a rate of 90 degrees in 0.25 seconds with a 30 KHz screen at a distance of 2 meters. The radial swept distance is 5.23 meters, for a rate of 32.86 meters / second. Call it 30 meters / second.

At 30 KHz, the step distance per flicker cycle is (30 meters / second) / (30000 cycles / second) = 0.001 meters / cycle, or 1 mm / cycle at a distance of 2 meters.

Seems within reason enough.

[Marco]

120Hz LED is a totally different beast. It has zero persistence

The language of LED tvs has never been very precise, but generally 120 Hz means motion compensated with capture and hold (so full persistence between frames).

240 Hz used to generally mean 120 Hz motion compensated with the backlight only on for a short time.

[ocset]

This is taking your ignorance to a whole 'nother level. How the f**k are you working as an engineer at a lighting manufacturer when you demonstrably know nothing about electronics or lighting?!?

Thanks, OK, i was workigng at a lighting manufac.......my contract expired two weeks ago....i have now been placed on a max 6 month contract, and my pay reduced by 25%, and i am only now here until  i handover to the next engineer.

[NiHaoMike]

I wonder if his insistence of not using electrolytic capacitors at all is making it difficult to make the lights flicker free and within budget.

[Tomorokoshi]

I like to know about the one who claims to be able to see flicker at 30kHz. In PC gaming, 144Hz is a popular choice for high end monitors and anything more is considered far into diminishing returns.

Let't calculate.

You sweep your eyes at a rate of 90 degrees in 0.25 seconds with a 30 KHz screen at a distance of 2 meters. The radial swept distance is 5.23 meters, for a rate of 32.86 meters / second. Call it 30 meters / second.

At 30 KHz, the step distance per flicker cycle is (30 meters / second) / (30000 cycles / second) = 0.001 meters / cycle, or 1 mm / cycle at a distance of 2 meters.

Seems within reason enough.

My limit is 3 KHz with an LED driven by a 20% duty cycle square wave.

[james_s]

Any info you can share on this??

On what? The NuColor display, or my reaction to it? There is plenty of info out there on the display, it's used in all of the color TDS500, 600, and 700 series scopes from the 90s.

[Zero999]

It seems plausible that many people find flicker uncomfortable. There are some unfiltered LED lamps at my parents' house and I do notice the flicker. It's not too bad, when there are other filtered lamps on though.

Flicker can be dangerous around rotating machinery, as an object spinning at 6000rpm will appear stationary in a light flickering at 100Hz.

[Siwastaja]

Those who are bothered by 120Hz flicker must have had a really bad time back in the days of 60Hz TVs. There are also 240Hz monitors and TVs out there, but they're mostly for 3D glasses so that the effective framerate would be 120Hz after the glasses demultiplex it.

CRT phosphors do not blank out immediately. Actually, the raster scan happens for infinitesimally short time at each phosphor site, but the persistence of the phosphor makes it glow even when not exposed to the electron beam. If you turn off the lights in the room, then turn off the TV, you'll see that some persistence is there even for 10-15 minutes!

Basically, phosphors varied case-by-case. Some 60Hz CRTs can be as non-flickery as standard lightbulbs, while some flicker a lot. Computer monitors tended to use quicker phosphors, requiring refresh rates up to 85Hz to provide flicker-free image.

[tooki]

Any info you can share on this??

On what? The NuColor display, or my reaction to it? There is plenty of info out there on the display, it's used in all of the color TDS500, 600, and 700 series scopes from the 90s.

Info on the display. But with the name I can now google it. Thank you!!

[BrianHG]

Count me as a 100hz hater.  Even on 50hz European CRT.  In fact, I had super expensive progressive 120hz desktop screens and a 40 inch 90Hz computer monitor as a television with scan rate accelerator since the beginning of 2000 and never looked back.  Older on chip DLP projectors were impossible for me to look as including full color LED billboards which are configured only around 180hz.

My partner never saw a thing.  He was happy with 60hz computer screens.  So, you can say that some people just have faster response retinas in their eyes.

120hz lighting is borderline for me today, if I had to drive in 100hz lighting, I would throw up...

[JPortici]

FWIW i am sensitive to flicker. I get strong headaches
- From fluorescent lights, but that may also be correlated with the wwhite tint, glare..
- From LED headlight from certain auto manufacturer, mainly BMW and earlier Alfa Romeo. Seriously, sometimes i think i can see a hint of the sequence, like when you make a video and watch it back
- it if i see a 3d movie, plus i have a very low perception of 3d altough i don't know if it's correlated.
- from monochrome CRTs. Scopes, early monitors always gave me big headaches. see my previous thread -> https://www.eevblog.com/forum/chat/sickness-from-monochrome-crts/

one thing for sure, in some environments you mustn't underestimate stroboscopic effect like when dealing with machinery.

regarding street lights, yeah i can very easily see them flicker. LED lights were a blessing, but not because they don't flicker.. because they are much more effective! the target area is REALLY illuminated, the surroundings are not (which can be a good or bad thing)

[ocset]

FWIW i am sensitive to flicker. I get strong headaches
- From fluorescent lights, but that may also be correlated with the wwhite tint, glare..

Thanks JPortici, but i  feel i must tell you that the actual light output of  old magnetic ballast fluorescent lights does not flicker.....because of the luminescance of the fluorescent gas in the tube...it stays lit even when the current through it goes to zero.........so the fluorescents do not flicker.

[Siwastaja]

Fluorescents do flicker quite a bit - I have measured the fact myself.

An easy way to measure is to take a digital camera capable of very short exposure time (such as 1/4000 s), then randomly take a shitload of images to give statistically significant number of samples; then just plot the occurence of different luminances.

With fluorescents, you notice an interesting thing when you do this: the color temperature flickers radically as well.

[ocset]

Fluorescents do flicker quite a bit - I have measured the fact myself.

Thanks yes but the light doesnt go anywhere near zero...the current does, but the light doesnt....fluorescents are like "CFD <25% " in this site..
https://www.derlichtpeter.de/en/light-flicker/cfd/

So for fluorescents the flicker index (CFD)  is less than 25%...which is said to be "rarely perceptible to humans"

Fluorescents do flicker quite a bit - I have measured the fact myself.

Thanks,i searched the web and its not possible to find a light output waveform diagram for a fluorescent.

It is needed info, as per this page provided kindly by earlier contributor (thankyou maukka)
https://www.derlichtpeter.de/en/light-flicker/cfd/


....this page says that if CFD (flicker index) is >50% then it is illegal for indoor or outdoor work illumination....but i cant find the bit in DIN EN 12464 where it actually  says that its illegal...do you know where it says this?

The website just above says that the worst case of flicker (CFD>100%) IS "Hazardous according to DIN EN12464  and must be avoided" ...but then goes on to say that it's a desirable thing to have in discoteque's...............hmmmm...is this thing really hazardous then?......its ok in discoteques......how many discos have hazardous light warnings.

I am sensing that there is a lot of old cobblers going on here....aren't you?

regarding street lights, yeah i can very easily see them flicker. LED lights were a blessing, but not because they don't flicker..

Thnaks, but again the old sodium vapor streetlamps did not flicker...the luminescance carried on throughout the zero current intervals.

..............................
A survey was actually done in a busy shopping street in  Manchester in winter, .....streetlights using SMPS’s with outputs which were PWM dimmed at 100Hz and duty of 50% were used….at the end of the street, people were asked  (3000 people total) if they noticed the flicker in the streetlights……in virtually all cases…the people actually said they didn’t even notice the  fact that there were streetlights….there was no extra  illumination from shop front lighting in that particular street.

[helius]

I have an older TDS scope with a sequential color display and normally it looks fine to me but if I try to use it when I'm very tired the flicker is pronounced and gives me a headache. I still love that display due to the novelty though, full color out of a B&W CRT with no shadow mask, it's neat, but that's off topic.

Any info you can share on this??

Tektronix used a sequential-color system that was branded/licensed NuVision. The CRT was an ordinary monochrome tube with a single electron gun, but with a LCD filter stack in front of it. As the liquid crystal cells switched on and off, they steered the polarization of light through colored polarizers, one per color field. It was found on some TDS scopes and certain other products like virtual reality HMDs.
There was another wild color technology based on electron beam overpenetration. The phosphor on the tube face was applied in multiple layers, each layer a different color. The electron beam energy determines how far into the phosphor layer the electrons can penetrate, which enables multiple colors. This was found in some HP and Tek displays.

Part of what makes these techniques interesting is that they enable true vector displays in color.

[Gyro]

Tek Nuvision always gave me problems. It was a lovely image if you looked at it straight-on (as long as my eyes weren't flicking backwards and forwards too much) but if I was soldering something on the bench it played hell with my peripheral vision.

I don't know what multiplexing rate they used (presumably LCD shutter response time limited) but it certainly wasn't fast enough.

[NiHaoMike]

There are LCDs that implemented color with a RGB backlight rapidly cycling through the colors, but it never caught on due to the difficulty of making a LCD fast enough for that to work well. Without the color filters blocking 2/3 of the light, it even had a black and white mode that used only ambient light, competing with Eink displays.

[janoc]

I wouldn't call myself "sensitive" to the flicker but 50-100Hz flicker can be (and is) a problem in certain situations.

- Office workers. Flourescents are terrible and not recommended anywhere where people work with computers. The flicker is alone invisible for most but it can "beat" against the backlight of the screen (which typically runs at 60Hz) and you get 10Hz flicker in your peripheral vision which is really annoying. Lot of people get a headache from this without even realizing.

- Any place where things are moving. Stroboscopic effect is very real and such lighting could be literally deadly - e.g. on a factory floor with moving/spinning machinery or airports. In fact, the airport staffers are specifically trained to look for signs whether an engine is running other than a spinning fan/propeller because those could appear stationary to them thanks to the strobing of the lighting. The results of missing something like that are a bloody and greasy spot

When it comes to LEDs those are even worse at 100Hz than flouros, because the phosphor in the flouros has a persistence and won't go off completely between cycles. On the other hand, LEDs will, so the strobing is more visible.

Don't be a cheapskate and build a proper driver for your LEDs so that they don't strobe on 100Hz.

Re flourescents supposedly non flickering - connect a photodiode to your oscilloscope and point it at the nearest florescent. You will see how "non flickering" the lamp is first hand.

This is taking your ignorance to a whole 'nother level. How the f**k are you working as an engineer at a lighting manufacturer when you demonstrably know nothing about electronics or lighting?!?

Thanks, OK, i was workigng at a lighting manufac.......my contract expired two weeks ago....i have now been placed on a max 6 month contract, and my pay reduced by 25%, and i am only now here until  i handover to the next engineer.

Sorry to hear but given your history here, I am frankly surprised they kept you on board even this long. Some of the things you have presented here were quite shocking even for a non-EE software guy like me.

[StillTrying]

Thanks,i searched the web and its not possible to find a light output waveform diagram for a fluorescent.

There's the shape of a 9W CFL's light here, center image.
www.eevblog.com/forum/chat/20w-halogen-bulb-viewed-by-a-photodiode/msg1316515/#msg1316515

Unfortunately I'd not recorded the 0% light level for that one, so don't know the p-p depth of the flicker.

[Siwastaja]

Thanks yes but the light doesnt go anywhere near zero...the current does, but the light doesnt...

Yes, this is true. According to my tests, the light output drops to around 10-30% of the maximum in the valleys. Which is a lot less than incandescents at about 70-90%. So, more flicker. But not horrible, like some (improperly driven) LEDs, which not only go to 0%, but also stay there for significant portion of the cycle.

So for fluorescents the flicker index (CFD)  is less than 25%...which is said to be "rarely perceptible to humans"

Which seems true as well - the incidences indeed seem "rare". As said before, I knew one guy. A few have popped up here. Not usual, but not non-existent, either. "Rarely perceptible", indeed.

What does this mean? Whenever possible, we try to build our public spaces so that you can access them with wheelchair, even though it's "rare" to be in one.

So, if you can design a light which is good for everyone and not just "most of the people", I think you really should. You'll make a better, more universal product with good karma, not causing problems.

A good aim is to have at least the same performance to the old fluorescents, or preferably a bit better. Add some extra margin, because it's difficult to directly compare these two technologies which will result in different "shape" of waveform.

It's worth remembering that if you don't actively keep this in mind, you can end up with orders of magnitude worse with LEDs. And this is not OK.

OTOH, as I said in my first post to this topic, it makes no sense to aim for perfection here. Old mains-driven fluorescents were "fairly OK". Aim for a bit better (like half the "flicker index") and you'll be fine.

As a side note, when talking about "fluorescents", we mostly tend to mean the old style of direct drive from the mains through an inductor ballast. In case of electronic transformers, including CFLs, some are practically flicker-free, some flicker, depending on how much capacitance they use after rectifying the mains.

[james_s]

Tektronix used a sequential-color system that was branded/licensed NuVision. The CRT was an ordinary monochrome tube with a single electron gun, but with a LCD filter stack in front of it. As the liquid crystal cells switched on and off, they steered the polarization of light through colored polarizers, one per color field. It was found on some TDS scopes and certain other products like virtual reality HMDs.

I don't think it used filters, my recollection is that somehow controlling the degree to which the liquid crystals rotated could control the wavelength of light it lets pass. At any rate there are no visible cells or pixels, the filter appears as a single continuous window and allows a really unique looking display. It has the razor sharp monochrome CRT look but in full color. If I'm tired the flicker is distracting but otherwise it looks great and it's so unique that the cool factor makes up for any deficiencies.

[ocset]

There's the shape of a 9W CFL's light here, center image.
www.eevblog.com/forum/chat/20w-halogen-bulb-viewed-by-a-photodiode/msg1316515/#msg1316515

Thanks, may i ask, do you mean in  the Reply #7 ?

[StillTrying]

"do you mean in  the Reply #7 ?"

Yep,  CFL.gif,  the link jumps to Reply#7 for me. The yellow trace is just to see where the mains peaks are relative to the light peaks.

[ejeffrey]

Those who are bothered by 120Hz flicker must have had a really bad time back in the days of 60Hz TVs. There are also 240Hz monitors and TVs out there, but they're mostly for 3D glasses so that the effective framerate would be 120Hz after the glasses demultiplex it.

CRT phosphors do not blank out immediately. Actually, the raster scan happens for infinitesimally short time at each phosphor site, but the persistence of the phosphor makes it glow even when not exposed to the electron beam. If you turn off the lights in the room, then turn off the TV, you'll see that some persistence is there even for 10-15 minutes!

Basically, phosphors varied case-by-case. Some 60Hz CRTs can be as non-flickery as standard lightbulbs, while some flicker a lot. Computer monitors tended to use quicker phosphors, requiring refresh rates up to 85Hz to provide flicker-free image.

CRT phosphors almost always have very short persistence times.  If you look at high speed photos of them, you will see that only a few of scanlines are actually illuminated at once.  Yes, you can have after glow for seconds or minutes, but that is a tiny fraction of the light.  Almost all of it is gone in IIRC, 100s of microseconds.

Plenty of people are bothered by CRT flicker as well, but probably less than from crappy LED lighting.  CRTs have a number of things working in their favor.  The first is of course that they aren't primarily intended for illumination.  A TV viewed from 10 feet away with other illumination in the room is much less likely to be perceived as annoying that if the room lights themselves (and everything else with it) are flickering.  Some people have problems with TVs in otherwise dark rooms.  In addition, because it is scanning the screen is usually emitting about the same amount of instantaneous light except during the vertical retrace, but that is only 1 ms out of a 16 ms field.  This is likely much less annoying than a light or backlight that is flashing completely on and off.  You might see bad flicker if you display a pattern where the top half of the screen is bright white and the bottom half is black but that isn't common or likely to persist long.  Finally, CRTs used for TV and movies typically are displaying live action, which can mask the flicker.  Flicker was definitely more of a problem for static computer screens (also more often viewed at close distance), hence the popularity of high speed computer monitors that could do 100 Hz+ frame rates without interlacing.

[ocset]

Yep,  CFL.gif,  the link jumps to Reply#7 for me. The yellow trace is just to see how where the mains peaks are relative to the light peaks.

Thankyou....the following page
https://www.derlichtpeter.de/en/light-flicker/cfd/

....top centre waveform, shows a magnetic ballast light output waveform, and i assume if your scope had been on DC , then it would have conformed to that? (ie troughs staying well above zero light)

[StillTrying]

https://www.derlichtpeter.de/en/light-flicker/cfd/

....top centre waveform, shows a magnetic ballast light output waveform, and i assume if your scope had been on DC , then it would have conformed to that? (ie troughs staying well above zero light)

My capture looks somewhere between the first 2 to me, I might do it again later, but it won't be with that same 9W CFL.

Edity. Added a CFL light plot complete with zero light level.
www.eevblog.com/forum/chat/20w-halogen-bulb-viewed-by-a-photodiode/msg1725482/#msg1725482

[tooki]

120Hz LED is a totally different beast. It has zero persistence

The language of LED tvs has never been very precise, but generally 120 Hz means motion compensated with capture and hold (so full persistence between frames).

240 Hz used to generally mean 120 Hz motion compensated with the backlight only on for a short time.

Yeah. Not talking about motion compensation (advertised 2000Hz my ass...), just about lighting and backlighting.

[mzzj]

Just my 2(euro)cents even if OP is silly troll:
Our bedside reading (led)lamps are really annoying, no flicker at first glance but every movement is jerky. Distracting at least.
1khz PWM with low duty cycle on flashlight can be also really annoying with fast movements.

[ocset]

Thanks, I am still working through all your excellent replys, and the links which you have kindly given.

Thanks to TwoFlower who gave the paper from Wilkins. This strategically avoided declaring any definite biological health risks of flicker......
https://www.ece.neu.edu/groups/power/lehman/Publications/Pub2010/2010_9_Wilkins.pdf
.....It said that the worst flicker was 3-70hz, and that this can sometimes occur in leds or fluo’s that have undergone some kind  of  failure giving unbalanced driving of the lamp.

Also, Derlichtpeter,
https://www.derlichtpeter.de/en/light-flicker/cfd/
….kindly given by Maukka, tells us that DIN EN 12464 actually bans high levels of 100Hz flicker for  indoor , or outdoor  work related use. It says that it is “hazardous for work and must be avoided”….but there was no mention of any law against using these kind of lamps. Surely if it was really dangerous then there would be a law against it?

Also, surely if 100Hz flicker is that bad, then the safety standard that pertains to it (EN 12464) would be free-of-charge…I mean, it would be inhumane to charge money for something that was needed for peoples safety….but perhaps 100hz flicker isn’t really dangerous after all?..so that’s maybe why they charge money for EN12464…  I would certainly like to see the section where it declares that 100Hz flicker at CFD >75%  is hazardous  and to be avoided. What is the penalty for seeling such products?…there was no mention of this…and surely there would be if it  really was hazardous?
I am afraid I just can’t believe it……there are loads of retrofit led light bulbs in the supermarkets that are compatible with phase cut dimmers……..and these produce really high levels of 100hz flicker…and yet these products do not have safety warnings on them…and are sold by the millions and millions.
If we are saying that 100Hz flicker is dangerous and hazardous…..then it would be illegal to illuminate roads with 100hz flickering streetlights…and this is not the case…loads of roads are illuminated thus, and there are no overly large incidences of accidents  on such stretches of roads.
Again, there would  be defined laws against  deep 100hz flicker if it really was as hazardous as declared. There would be stories of people going to prison for flogging deeply  100hz flickering lighting….these stories do not exist.
What I can see, is that there is a definite motive for spreading stories that 100hz flicker is hazardous…that is, the large electronics corporations have set out their stall to sell flicker-free led lighting  drivers in huge quantities…these comprise significant electrolytic capacitor banks which make it easy to do away with 100hz flicker…….and so what they then do, to kill off smaller companies trying to sell 100hz flickering lights, is spread stories that 100hz flicker is dangerous and hazardous.
I still fail to find actual laws banning 100hz flicker. There would be actual laws if it really was hazardous. If EN12464 really says  that 100hz flicker should be avoided due to health reasons, then surely EN12464  would be freely available, for reasons of humanity?

[BrianHG]

I do not want to drive down a highway at high speed where any rapid eye movements to an unexpected oncoming car, or an obstruction on the road leads to a stroboscopic visual effect.  My life is at stake traveling at high speed with unfamiliar moving objects (cars/trucks/motorcycles) around me controlled by other people.  WORSE, I don't want another driver on the road, who may be effected as well, crash into me because they are effected by the strobe just at the wrong time.  Just eliminate that stupid flicker.  We can easily do that much with today's technology.  In fact, we have the technology to replicate close to sun-light, what our eyes have been evolved to operate with.

We are not talking about a house light bulb where I'm causally walking around.  If it the effect is too bad for me personally, I can just simply buy a new different light bulb.

[Gyro]

Also, surely if 100Hz flicker is that bad, then the safety standard that pertains to it (EN 12464) would be free-of-charge…I mean, it would be inhumane to charge money for something that was needed for peoples safety….but perhaps 100hz flicker isn’t really dangerous after all?..so that’s maybe why they charge money for EN12464…  I would certainly like to see the section where it declares that 100Hz flicker at CFD >75%  is hazardous  and to be avoided. What is the penalty for seeling such products?…there was no mention of this…and surely there would be if it  really was hazardous?
...

 There would be actual laws if it really was hazardous. If EN12464 really says  that 100hz flicker should be avoided due to health reasons, then surely EN12464  would be freely available, for reasons of humanity?

Oh treez, you poor deluded soul 

There are many ENxxx standards that relate to safety - all the Low Voltage Directive ones for a start. It's nothing to do with humanity, standards cost money to develop. If you're a manufacturer you're expected to put your hand in your pocket and pay for them!


P.S. EN12464 is only £198 from the BSI store. It makes me wonder how many of the relevant standards your company has ever bothered to buy, let alone adhere to.

[james_s]

Frankly this is starting to piss me off. We have people here including myself stating as a fact that we find 100/120Hz flicker distracting and uncomfortable and this guy has his fingers in his ears yelling "LALALALALALALALALALALALA" and insisting over and over that nobody complains about it and it isn't a problem because apparently myself and others are nobody, and it's all some big conspiracy and blah blah blah.

Arg! You wonder why no respectable company will hire you and you're stuck at some backwards dump of a place! It's because respectable companies want to hire competent engineers who can design solid and dependable products that meet the criteria specified by the customer. Not someone who is relying on volunteers of a public forum to do their job for them, all the while bitterly complaining that the customer is full of shit should change their criteria.

[tooki]

You aren’t the only one getting pissed off. If treez isn’t just a master troll, then he’s an idiot.

One more thing to add about standards: just because there isn’t a standard now doesn’t mean that something isn’t a problem. It simply means a standard may not have been developed yet. LED is the first mainstream lighting technology with major flicker issues when done wrong. It’s only been around for a few years (LED indicators don’t count!), so the extent of how many people are bothered may yet be unquantified. But this doesn’t make the problem nonexistent!!!

Again, treez is exhibiting astonishing arrogance on this issue. But watch him continue to “like” every post that is critical...

[NiHaoMike]

If he gets rid of his insistence on no electrolytic capacitors, he'll suddenly find that making LEDs flicker free is quite easy.

[ocset]

Thanks, I remember the old days when we had triac dimmed incandescent  lighting. This had severely deep 100Hz flicker. However, there were never any complaints about it. Then Magnetic ballast fluorescent lighting came  in…. this had virtually no perceptible 100Hz flicker..however,  when the tubes were about to fail, they  often went into “non-balanced drive mode” and so they flickered at 50Hz……this indeed is visible, and is what started off all the problems with this flicker debate. People hated the 50Hz flicker of  failing magnetic ballast fluorescents, and so just pretended they could always see the flicker even when  it was at 100Hz and invisible…..in a desperation to just  get fluorescents banned.

Epileptic seizures are mostly caused at below 15Hz flicker, and never above 70Hz flicker. –Light shimmering off a wavy sea, or light fluctuating through windblown trees is a major causation of epileptic seizures due to the light flicker at <70Hz

Concerning  roadways  and  100Hz flickering  streetlights….Its not a problem in my opinion. There are far worse problems with  road use…eg Lack of visibility in certain makes/models of cars with too small rear windows etc….LED headlights being far too bright and blinding people, including being blinded from one’s rear view mirror……People having front lamps on full beam when an opposite side-of-the-road car is approaching (there should be sensors which turn a warning siren on when a car is approaching so the driver is reminded to go onto dipped beam)…..The need for fog sensors on roads so that drivers are fore-warned to slow down prior to reaching sudden fog patches….(this caused a  multiple tragedy in UK some years ago near Taunton). Car audio systems being banned because one has to  take eyes off the road in order to press on/off or change radio  station/ CD  etc, etc, Coffee cup holders banned from cars because again, when driving, you have to take your eyes off the road to put the coffee back in the holder….as such, drive-through starbucks being banned from the roads. All cars with acceleration above  0-60mph in 9 seconds banned. Cars capable of doing >90mph banned….”vigilante” cars should roam the  busy roads and the public be told they are in service…..so that they can catch people tailgating 1 metre behind when doing 70mph…..such tailgaters would be taken off the road and banned for a year to make roads safer…..so there are many things on roads which should be banned, but not streetlights  with 100Hz flicker.

Currently, major roadways and motorways are legal even with no streetlighting...and 100Hz flickering streetlit roads are far safer than totally unlit motorways.
..Some guys  backbox has fallen off and lies in the middle of the motorway…you want streeetlighting so you get to see it as soon as possible.....100Hz flicker streetlighting does this just as nice.

Those who are bothered by 120Hz flicker must have had a really bad time back in the days of 60Hz TVs.

Thanks, did all the old non-LED style TVs (ones with scanning tubes in them) flicker at 50Hz?

[tooki]

Fucking hell, dude... Dimmed incandescent doesn’t flicker the same as LED, because of the thermal low pass filtering of the filament.

You remain doggedly convinced that fluorescent flicker is a myth, when in fact some people do measurably react to it. Repeat. After. Me: “Just because I’m not sensitive to it doesn’t make it a myth!”

[james_s]

There's something else at play here too. Run from AC, LED output is not linear over the whole sine wave, dropping to zero only at the zero crossing. Once the voltage drops below a particular threshold the light output falls to zero, and remains zero until the voltage rises to a threshold on the next half cycle. Discharge lamps exhibit some degree of this effect but there is generally a wider range so the output spends significantly less time at zero and the edges are softer. Fluorescent does flicker some but due to phosphor persistence the edges are softer still. It still bothers some people but it is not nearly as annoying as flickering LEDs.

CRT TVs all did flicker to some extent, but they have some phosphor persistence and also the screen is only dark during the vertical and horizontal blanking intervals which are a small portion of the total time. In 50Hz countries most TVs used a 50Hz vertical frequency, over here they used 60Hz. CRTs are not used for general illumination either, which is another reason the flicker is less objectionable.

[glarsson]

What about the persistence of the phosphor in modern white LEDS?

I have managed to find LED lamps with E14 socket (not much space for a big capacitor) that has no visible flicker (and I am usually very sensitive to flicker).

[maukka]

The persistence is non-existent in LEDs. They can be PWMd at tens of kHz and they still emit no light in between.

Here's a Nichia 219B at 16 kHz as an example. Measured optically with a Thorlabs DET36A/M.

[tooki]

What about the persistence of the phosphor in modern white LEDS?

I’ve wondered about their characteristics too. They probably have some persistence, but it can’t be even distantly similar to that of CRT phosphors. In all fairness, they’re unlikely to be chemically that similar, since CRT phosphors react to electricity, vs reacting to light in LED and fluorescent phosphors.

[glarsson]

I tested with UV light from a UV LED  flashlight on a color TV CRT, monochrome monitor CRT, oscolloscope CRT and LED light bulbs. All of them was fluorescent.

I can't see any reason why LED phosphor can't have long persistence.

[StillTrying]

The persistence is non-existent in LEDs. They can be PWMd at tens of kHz and they still emit no light in between.

Yes, in my light experiments I've flashed a 5mm red LED at 1MHz, ~50mA@~2.1V, the detected light rise and fall times where about 75ns, and the light was fully on and fully off for most of the 500ns!

I originally started the experiment to see if I could detect any difference in the light switching speeds between phosphor and non phosphor LEDs, but got a bit diverted, so far I've only detected a slight slowness in quite warm coloured white LEDs, but only a us or two, nothing that would be eye detectable.

[Domagoj T]

Flashing lights are a part of EEG (Electroencephalography), or at least the kind that I had to do as a part of larger medical exam for a job application. I don't have epilepsy and was a perfectly healthy 20 something year old at the time, but that strobe light sure was uncomfortable and I would not want that to be part of my everyday life.

[ocset]

I  would love to hear  your opinions on a nightclub where I  used to work………there were 1000’s  of people in there…and the entire  lighting was flashed ON/OFF at frequencies from 10Hz to 100Hz……that’s going from max brightness to absolute darkness at those frequencies……we would sweep between those frequencies over a few seconds…………absolutely amazing effect…everybody loved it….nobody ever complained…nobody left the club during the sweeping, flickering  light………………it was the most severe  flicker ever….beautiful!

The one thing that sounded like it was going to stop 100Hz flickering streetlights was dash cams on police cars…but in fact, this is easily mitigated and modern police dash cams don’t have any trouble whatsoever with 100Hz flickering streetlights.

[Siwastaja]

I  would love to hear  your opinions on a nightclub where I  used to work………there were 1000’s  of people in there…and the entire  lighting was flashed ON/OFF at frequencies from 10Hz to 100Hz……that’s going from max brightness to absolute darkness at those frequencies……we would sweep between those frequencies over a few seconds…………absolutely amazing effect…everybody loved it….nobody ever complained…nobody left the club during the sweeping, flickering  light………………it was the most severe  flicker ever….beautiful!

It really didn't pop into your mind that maybe people who are sensitive to flickering lights don't visit the nightclubs for the obvious reason?

[Echo88]

The starting post shows that theres no way to win an argument with this person, since he doesnt accept changes in his views.

[tooki]

I  would love to hear  your opinions on a nightclub where I  used to work………there were 1000’s  of people in there…and the entire  lighting was flashed ON/OFF at frequencies from 10Hz to 100Hz……that’s going from max brightness to absolute darkness at those frequencies……we would sweep between those frequencies over a few seconds…………absolutely amazing effect…everybody loved it….nobody ever complained…nobody left the club during the sweeping, flickering  light………………it was the most severe  flicker ever….beautiful!

The one thing that sounded like it was going to stop 100Hz flickering streetlights was dash cams on police cars…but in fact, this is easily mitigated and modern police dash cams don’t have any trouble whatsoever with 100Hz flickering streetlights.

Ummm, a club isn’t the same environment as a road or home. Try driving with that shit flashing around you - it’s awful. (Yes, modern LED police lights are, IMHO, dangerously distracting. FAR worse than the old incandescent ones.)

Or try reading something in a club.

Jesus, man, you are dense...

[james_s]

I loathe nightclubs, the lighting isn't the only reason but it makes me intensely uncomfortable. Are you really that stupid or are you just pulling everyone's leg for some reason?

[Gyro]

I  would love to hear  your opinions on a nightclub where I  used to work

That could explain a lot - from nightclub headbanger to the world worst electrolytic-free LED luminaire designer! 

It could explain the deafness too.

[ocset]

It looks like we are all off course.....according to this,  all LED lighting is extremely dangerous whether or not it flickers...this is because of the Reactive Oxidative stress caused by the high blue light content of LEDs......

https://articles.mercola.com/sites/articles/archive/2016/10/23/near-infrared-led-lighting.aspx

[tooki]

It looks like we are all off course.....according to this,  all LED lighting is extremely dangerous whether or not it flickers...this is because of the Reactive Oxidative stress caused by the high blue light content of LEDs......

https://articles.mercola.com/sites/articles/archive/2016/10/23/near-infrared-led-lighting.aspx

That’s an alternative medicine crackpot. That “article” opens by saying that only 1/3 of our energy comes from food, and the balance is infrared. Apparently he believes we are ectothermic (cold-blooded) like reptiles...

Anyway, does this mean you’ve accepted that flicker is an issue, or are you stuck on “it don’t bother me, so it ain’t no thang!”??

[helius]

CRT TVs all did flicker to some extent, but they have some phosphor persistence and also the screen is only dark during the vertical and horizontal blanking intervals which are a small portion of the total time.

CRT phosphors almost always have very short persistence times.  If you look at high speed photos of them, you will see that only a few of scanlines are actually illuminated at once.  Yes, you can have after glow for seconds or minutes, but that is a tiny fraction of the light.  Almost all of it is gone in IIRC, 100s of microseconds.

The post from ejeffrey is correct. If they used a longer persistence phosphor, motion blurring would be unacceptably great. (Much like old passive LCD displays where the mouse cursor left a long trail as it moved.)

Computer displays have sometimes used longer persistence phosphors: See the Xerox Alto Technical Report, which discusses the use of P40 phosphors with longer persistence for better ergonomics. The display was interlaced at 60 fields per second. Such a display was not designed for moving pictures (multimedia was over a decade away) so this was a good compromise when the display update speed was limited by memory technology.

[james_s]

They don't have a lot of persistence, but like I said they have *some* persistence. When I shut off a monitor in a dark room I can see a faint glow for several seconds. Looking at a high speed video of a CRT I see persistence. At least an order of magnitude dimmer than the active scan line but it is there and helps to soften out the edges. It's not a sharp on-off like you get with LEDs.

The main thing that helps though is as he said, the average illumination level is fairly constant. Since the blanking intervals are much shorter than the average picture time, the duty cycle is quite high even though only one spot is brightly lit at any instant.

[In Vacuo Veritas]

You aren’t the only one getting pissed off. If treez isn’t just a master troll, then he’s an idiot.

He's an idiot. How he got employment is strange, but how he kept it is a miracle.

[tooki]

You aren’t the only one getting pissed off. If treez isn’t just a master troll, then he’s an idiot.

He's an idiot. How he got employment is strange, but how he kept it is a miracle.

Oh, the latter is easily explained, if the stories he tells about management there are accurate: they're absolute morons, too…

[cdev]

There is something called the critical flicker frequency and human perception of when a blinking light becomes continuous varies quite a bit due to biological parameters.

https://www.ncbi.nlm.nih.gov/pubmed/?term=%22critical+flicker+frequency%22

(Also, bright blue LED light is unhealthy to your eyes. (I say as I sit in front of a monitor)

I should turn it down at night or something.

[John B]

This is probably echoing what has already been said, but my own experiments have lead me to avoid PWM dimmed LED lights altogether. I have a torch which has a reduced light setting around 30% duty cycle at 100Hz. I would consider the light quality to be awful, the flicker is terrible and it's annoying even when focusing on the light. I have a cheap LED dimmer which runs at around 300Hz, which is almost acceptable when looking directly at the light, but the peripheral vision effect was very noticeable. From ones that I've built myself, all those effects were gone around 3kHz. However I ditched them all because of EMI affecting audio equipment.

[cdev]

Most people myself included have a critical flicker frequency - that varies- - however some drugs, specifically the dilating eye drops (probably atropine or scopalamine) my ophthalmologist gives me when I get my eyes looked at, raise that frequency substantially, making me able to see and be annoyed by, the flickering of fluorescent and other lights. Its a wild and strange experience to be able to see lights flickering you don't normally see doing that.

[StillTrying]

I've pointed my photo diode at a 6 inch BW TV.
As the photo diode is looking at 12-15 lines I had to interpret, but the persistence of lines in a bright white area seems to be only about 100us before it's back to near enough the black level. I thought the persistence would be longer than that. - it's less than 2 lines!

[ocset]

Thanks, i wish we could have photo-diode checks on these new LED filament bulbs which are now selling by the multi-millions in UK........

https://www.thelightbulb.co.uk/light-bulbs/led/filaments?gclid=EAIaIQobChMI5uKYo4L33AIVDCjTCh2pLgGGEAAYASAAEgI3CvD_BwE

...These have a very high level of severe flicker at 100Hz..but there are no complaints  about them.

[StillTrying]

Thanks, i wish we could have photo-diode checks on these new LED filament bulbs which are now selling by the multi-millions in UK........
...These have a very high level of severe flicker at 100Hz..but there are no complaints  about them.

I might buy one in the next week, unless someone else tries it, a photo diode + 2k2 resistor would do for <1kHz, or PD + any 100mA transistor will do for <50kHz, and be cheaper than the LED bulb.

[Siwastaja]

...These have a very high level of severe flicker at 100Hz..but there are no complaints  about them.

There are a lot of complaints about them.

I have complained about them, and I'm not too sensitive to flicker.

Everybody complains about them all the freaking time.

Had one in a hacklab toilet and it was there only for a few days before it was replaced. No one could stand it - even if only exposed for it for short times. It was a great discussion starter really.

BTW, they are not all equal, either!

But if you decide to go "LA LA LA!! NOT LISTENING", then I guess there are no complaints about them, for you.

Yes, crap electronics is being produced and sold around the world in multi-millions. No, it's not a good excuse to design more crap. Especially if you are not targeting the $1-$2 segment!

Also, designing cheap crap is more difficult than you think. If you go too low, you'll hit problems soon. Your attitude is not going to work here. You need competency - the idea of the cheap crap is that you can spend money on R&D because they'll be sold in millions. Some $1 product may have $10000 extra engineering cost went in just to reduce the unit price by a few cents!

[james_s]

Those LED filament bulbs do tend to flicker badly, it's a fatal flaw that has severely limited my adoption of them. I have found some that have little enough flicker to be acceptable in a few applications but even so I don't use them for task lighting that I spend a lot of time under.

The level of denial is frankly stunning. We have what, 4 or 5 people just on this thread which is a very random esoteric corner of the internet complaining about the flicker which means there are likely tens of millions of people in the general public who find it bothersome and yet that's nobody? Honestly I envy those who cannot perceive flicker.

[NiHaoMike]

Big Clive does a lot of LED teardowns and it seems like the ones that flicker a lot do so very badly on video, but not all LEDs that flicker on video flicker to an annoying degree in real life. So I would say that it causes the most headaches for those filming videos.

Still, there's little reason for a quality LED light to flicker.

[BrianHG]

I've pointed my photo diode at a 6 inch BW TV.
As the photo diode is looking at 12-15 lines I had to interpret, but the persistence of lines in a bright white area seems to be only about 100us before it's back to near enough the black level. I thought the persistence would be longer than that. - it's less than 2 lines!

Careful here, that super quick charge of the phosphor actually fast charges way too bright to for your eyes to see properly if your eye could register that amount of light that quickly.  It's the initial fast discharge of the phosphor's decay process which means the actual light of the picture your eye accounts for a visual image, where the display is already down to around 5-10% of the charge brightness.  Since phosphor is a decay in brightness, not a linear drop in brightness, that last 5-10% which your photodiode is registering the light as black after the super-bright quick initial charge, after around 5 lines, is what your eye mostly sees which glows down to around 1-2% brightness at 1/60th of a second.  Remember, our eyes register light logarithmically, not linear like your photodiode.  You also need to take that into account as well.

Try amplifying your photo diode's output and ignore the initial phosphor charge during the first 4 line as the raster scans so you can see the remainder of the light.  After an initial cliff like drop in brightness, you will see a smooth curve developing over 1/60th of a second, actually it's even slower than that if you have 1 frame white, the next black, you will detect a decaying glow for 1/30th of a second (we are talking below 1%).  This is the light your eye is responding to.

[helius]

[The] quick charge of the phosphor actually fast charges way too bright to for your eyes to see properly if your eye could register that amount of light that quickly

Does this make any sense at all? There is no minimum period for light to be visible to your eyes. A strobe lamp has an emission lasting some tens of microseconds, but it doesn't cease to be visible. Sonoluminescence experiments produce flashes as brief as picoseconds and are visible to the naked eye.

[BrianHG]

[The] quick charge of the phosphor actually fast charges way too bright to for your eyes to see properly if your eye could register that amount of light that quickly

Does this make any sense at all? There is no minimum period for light to be visible to your eyes. A strobe lamp has an emission lasting some tens of microseconds, but it doesn't cease to be visible. Sonoluminescence experiments produce flashes as brief as picoseconds and are visible to the naked eye.

Careful, the strobe lamp is 10 times faster, but, 1000x stronger...  If you could keep a Xenon strobe tube on at full 50-100 amps, (approximate power of a good strong strobe during the short pulse), not only will you melt/burst the strobe tube, but, you would burn out your eyes and give you sunburn.  Just so we are clear, with a 3.5us flash, you feel heat coming from one of those Xenon tubes.  Keep it illuminated at that 50 amps continuously, the brightness will blind you in under a second.

I've done precise timing studies on monitor phosphor charge and discharge times, and even had super fast LCD shutters to block the light to the eye during the time the phosphor is being charged for around 15 lines of video.  Blocking the display during this charge time only, to the eye, the picture in that region dims only by around 15%.

The work I've done analyzing CRT phosphor was use in testing and creating my 3D stereoscopic patent here: https://patents.google.com/patent/US6532008

[ocset]

Hello,
Regarding  LED streetlighting flickering at 100Hz…..this would only affect  night-time security cameras and traffic cameras, and police dash-cams,  including number plate recognition cameras,  if the shutter speed was slower than 1/100th of a second  (10ms).
So do you know what is the shutter speed of these type of  security cameras? The www  doesn’t  tell.
Obviously, a Frame Rate of  25 per second, and a shutter speed of 1ms could  potentially record for a long time in the prescence of 100Hz flickering LED  streetlighting and show nothing at all (total blackness).
However, if all such security cameras automatically increase  shutter speed to  take in enough light, then this could be overcome…because going up to 10ms shutter speed would solve the problem…however, if this shutter speed is too slow for a fast moving object, then there would be movement blur. A man running at 10m/s  travels 10cm in 10ms….that could cause unacceptable movement blur…and it would be even worse for a vehicle which moves faster.
Maybe all such security cameras automatically shift the phase of the “shutter openings” in order to accommodate the effect of 100Hz flickering streetlighting with fast shutter speeds? (ie time it so each shutter opening corresponds to the mains peak point, where the flickering light is most bright)