100Hz flicker in lighting is a problem?

[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...