Beware of LED bulb flicker?

[Tom45]

http://www.dailymail.co.uk/health/article-4739766/Low-energy-LED-lightbulbs-giving-HEADACHES.html

Another thing to worry about?  "Professor Arnold Wilkins, professor of psychology at the University of Essex" says "While fluorescent lights, such as those in offices, dim by around 35 per cent with every flicker, LED lights dim by 100 per cent."

That is the first I heard about this "problem". And I haven't noticed the flicker myself.

So I measured a couple of different LED bulbs, both 100 watt "equivalent".

The flicker is there (120 Hz), but only about 5%, not 100%. Using a photodiode the level was about 300mv with 15mv p-p ripple on top of it.

Are there LED bulbs that really do go between 100% and 0%?

[kalel]

http://www.dailymail.co.uk/health/article-4739766/Low-energy-LED-lightbulbs-giving-HEADACHES.html

Another thing to worry about?  "Professor Arnold Wilkins, professor of psychology at the University of Essex" says "While fluorescent lights, such as those in offices, dim by around 35 per cent with every flicker, LED lights dim by 100 per cent."

That is the first I heard about this "problem". And I haven't noticed the flicker myself.

So I measured a couple of different LED bulbs, both 100 watt "equivalent".

The flicker is there (120 Hz), but only about 5%, not 100%. Using a photodiode the level was about 300mv with 15mv p-p ripple on top of it.

Are there LED bulbs that really do go between 100% and 0%?

With a Joule Thief circuit and a small self color changing RGB LED, I noticed that it stays at the first color constantly (without a capacitor added). Now, I don't know if it needs to drop to 0 for that to happen. But Joule Thief (without or even with a capacitor) is not the standard power supply case.

[MK14]

http://www.dailymail.co.uk/health/article-4739766/Low-energy-LED-lightbulbs-giving-HEADACHES.html

Another thing to worry about?  "Professor Arnold Wilkins, professor of psychology at the University of Essex" says "While fluorescent lights, such as those in offices, dim by around 35 per cent with every flicker, LED lights dim by 100 per cent."

That is the first I heard about this "problem". And I haven't noticed the flicker myself.

So I measured a couple of different LED bulbs, both 100 watt "equivalent".

The flicker is there (120 Hz), but only about 5%, not 100%. Using a photodiode the level was about 300mv with 15mv p-p ripple on top of it.

Are there LED bulbs that really do go between 100% and 0%?

I think (based on what BigCliveDotCom's youtube video says, so I could easily be wrong).

But supposedly, the newer LED bulbs or lighting, may start to have NO capacitors in them (new designs, probably to reduce production costs). These therefore, may well have 100% on/off, flicker (or whatever you want to call it).

But they maybe only for outdoor use, I'm not sure.

tl;dr
New one piece LED "chips", without much/any capacitance, to hold the LEDs on, during the off (low voltage) parts of the AC mains cycle.

N.B. I could easily be wrong. I only have weak information about it at the moment.

tl;dr2
What I mean is that the old/existing LED lamps have controllers as well as the LEDs. The newer type, ONLY has the LEDs, the controller is built into the LEDs (chip on board, COB), but hence has little/no capacitance. Hence the 100% on/off flicker situation.

tl;dr3
Hopefully only a minority of future LED bulbs will be the high flicker type. So that if you buy decent bulbs at reasonable prices, they will have minimal/reasonable flicker.

[georges80]

http://www.dailymail.co.uk/health/article-4739766/Low-energy-LED-lightbulbs-giving-HEADACHES.html

Another thing to worry about?  "Professor Arnold Wilkins, professor of psychology at the University of Essex" says "While fluorescent lights, such as those in offices, dim by around 35 per cent with every flicker, LED lights dim by 100 per cent."

That is the first I heard about this "problem". And I haven't noticed the flicker myself.

So I measured a couple of different LED bulbs, both 100 watt "equivalent".

The flicker is there (120 Hz), but only about 5%, not 100%. Using a photodiode the level was about 300mv with 15mv p-p ripple on top of it.

Are there LED bulbs that really do go between 100% and 0%?

Ah, professor of psychology, yep, and reported in a newspaper, check, must be true (hard) science

Maybe with a LED wired directly across AC, but any decent 'bulb' has an electronic ballast (high frequency switcher) and will compensate for most the AC cycle by keeping the LEDs fully driven. Then add in the caps used in the ballast and then factor in that the LED phosphor takes quite a few milliseconds to go off completely.

So, the 100% off would be quite an engineering challenge to achieve (with white LEDs).

There's a heck of a lot MORE flicker with non-electronic ballast fluoros.

Simple flicker test is to quickly move (back and forth) your open hand with fingers spread between your eyes and a LED/Fluoro etc light source - easy to see any strobe effect if the flicker is large magnitude.

cheers,
george.

[MK14]

In this one, he shows it with and without the capacitor. I.e. one flickers and the other doesn't flicker much.
Unfortunately, the one he reviews is suppose to NOT have the anti-flicker capacitor.

[Tom45]

tl;dr2
What I mean is that the old/existing LED lamps have controllers as well as the LEDs. The newer type, ONLY has the LEDs, the controller is built into the LEDs (chip on board, COB), but hence has little/no capacitance. Hence the 100% on/off flicker situation.

Interesting video tear down.

Lets hope that this design with no capacitor doesn't become widespread.

[MK14]

tl;dr2
What I mean is that the old/existing LED lamps have controllers as well as the LEDs. The newer type, ONLY has the LEDs, the controller is built into the LEDs (chip on board, COB), but hence has little/no capacitance. Hence the 100% on/off flicker situation.

Interesting video tear down.

Lets hope that this design with no capacitor doesn't become widespread.

It probably costs relatively little to add the capacitor (but it could be expensive, bigger capacitors at higher voltages, can be expensive), and get a nice, relatively non-flickering LED bulb/lighting. Even if it does cost a fair bit. It is probably well worth the money.

But in practice, I fear that many people, will try and buy the cheapest possible LED bulbs that they can.
E.g. buy them at a $1 store, or because it is $1.99 each, somewhere.

Therefore, if they produce these really cheap, capacitor free, LED lamps. Also because many people CAN'T see or perceive the flicker. They will sell in HUGE quantities.

Basically, my experience of people, is that they will try and buy the cheapest possible LED bulbs they can. I can try explaining to people that spending more, can actually be cheaper because they may last longer, be more reliable and give better quality light (e.g. colour temperature).
But I suspect they will still go out and buy the cheapest, LED bulbs, available for sale.

[IanB]

White, high brightness LEDs use a phosphor that is excited by blue/UV light, similar to fluorescent tubes. So the extent of the flicker will also depend on the persistence of the phosphor as well as the drive circuit. There is a gap of between 4-5 ms between the peak of the AC cycle and the next zero crossing. Will the phosphor lose all light emission during that interval? I do not know.

[MarkS]

Something tells me he read about PWM being used to dim LEDs and made the leap.

[georges80]

White, high brightness LEDs use a phosphor that is excited by blue/UV light, similar to fluorescent tubes. So the extent of the flicker will also depend on the persistence of the phosphor as well as the drive circuit. There is a gap of between 4-5 ms between the peak of the AC cycle and the next zero crossing. Will the phosphor lose all light emission during that interval? I do not know.

Like I wrote above. Yes, the phosphor helps a lot. Any DECENT bulb has an electronic ballast. The LEDs won't turn off just because the AC has come off the 'peak'. There's only a significantly shorter period of time where the voltage is lower than the LED + ballast operating voltage.

I purchase only Cree bulbs - the CRI (of the warm whites) is fantastic and I haven't had a failure yet and a few are on at least 6 hours per day every day and are at least 4 yrs old. Spend once and get something decent or buy $1 garbage - consumer choice.

The video above shows one of the cheap panel LEDs (typical of chinese flood lights etc), you get what you pay for in terms of ballast design (or none...).

Of course a cheap implementation will have even worse visible flicker at 50Hz vs 60Hz.

cheers,
george.

[Someone]

White, high brightness LEDs use a phosphor that is excited by blue/UV light, similar to fluorescent tubes. So the extent of the flicker will also depend on the persistence of the phosphor as well as the drive circuit. There is a gap of between 4-5 ms between the peak of the AC cycle and the next zero crossing. Will the phosphor lose all light emission during that interval? I do not know.

The phosphors used on white LEDs unlike the historical ones used in CRTs have extremely short time constants in the sub ms to us region, anything shorter is blurred by the slow speed of the exciting LED. Recall that white LEDs are used as flashes for phone cameras (although they tend to be specialty parts).

[Buriedcode]

Well, the 'Daily Mail' is probably the worst paper for scare-mongering and pseudo-science in the UK (every day warns that something causes cancer, whilst something natural cures it, and generally just tries to blame everyone's ails on some trendy scapegoat subject like wind farms, "chemicals" or political correctness). 

Also, psychologists have a way of coming up with theories and studies that can't be replicated, as such, more than any other science, its findings and theories should be taken with a huge pinch of salt

With that said, I do believe flickering lights can cause headaches - lots of things can cause headaches, especially lighting. (examples include, diet, posture, gait, asking someone if they have a headache - a good proportion will have a headache when you ask them).

As to whether its all LED bulbs (unlikely), how noticeable the flicker is, how many will be negatively affected, its anyone's guess.  Whilst I'm sure there will be some LED bulbs sold that will have noticeable flicker - it seems to be the source (the daily fail) is implying its ALL LED bulbs.

[NiHaoMike]

A lot of LED backlit TVs intentionally strobe at 120Hz or higher to reduce motion blur. Basically, if the LCD transitions only while the backlight is off, the user doesn't see it. The result is a display more like a CRT or plasma.
https://www.blurbusters.com/zero-motion-blur/lightboost/

Where 75Hz and greater flicker can cause headaches is if you're trying to film stuff.

[Chalcogenide]

A type of LED bulb that for my experience is very bad in terms of flicker is the one with the so-called "LED filaments". The LEDs are in series, thus requiring high-ish voltage (90V per filament or so), and manufacturers often save money by using a capacitive dropper supply with very little filtering capacitance, or none at all. I bought few of them to use in the living room but I could "feel" that something was wrong. When I checked for flicker, they were essentially off for half of the time... I had to move them to a room where I didn't spend as much time in, and replace them with "normal" LED bulbs.

[Kjelt]

It might be very personal, some persons are very susceptible to these things but will soon notice it.
For instance with single DLP projection systems where there is a colorwheel and the colors are projected in very high frequency one after the other about 10% of the people have the rainbow syndrome where their visionary system is able to see the different colours instead of the total picture causing headaches and nausia.
Now for the led lighting, probably with cheaper ledlighting where no fancy driver is used for cost down this might cause problems for some people, i would not be surprised.

[Kleinstein]

They could reduce the flickering a lot by combining one such led chain with current limiting and one with a capacitive dropper. Still the large capacitor needed (more like 5-10 µF range, like the motor caps) could be a cost factor. For a first test one could use 2 of such modules, one with a capacitor in series.

With large installation of old style florescent lamps they used this to improve the power factor and reduce the flicker.

[madires]

AFAIK the series cap in old fluorescent lamps is just for compensating the phase shift by the ballast. Our electricity providers demanded that for large installations of fluorescent lamps. Today's fluorescent lamps got electronic ballasts with a proper power factor.

[Vtile]

I'm not commenting in other parts of this than that the flicker of the light source is studied phenomenom. In fluerescent lights mainly in office and school environments which is lightly connected eye distress and that sort of thing. This from memory and this is not my area of interest, but I just to want to point out that the flicker is studied even before led became mainstream.

[tooki]

Yep. With LEDs, it's just more pronounced because of their essentially instantaneous response time (compared to the low pass filter effect of a heated filament or slow phosphors in fluorescent lamps).

FYI, the main problem (for me) with flickery LEDs is the "phantom array" effect. It's also responsible for the DLP rainbow problem, which I definitely notice readily. It doesn't cause me headaches, but it is highly distracting.

[RGB255_0_0]

It's an issue with LCDs too. And was a major problem with CRT monitors. Towards the end of CRT tech we got higher refresh rates to help a bit. Drooling over those Trinitrons...

If I was that bothered by it I'd look at changing the driver to constant current.

It's not an easy fix for mains powered led bulbs that need to fit a small package.

[MK14]

There are all sorts of complaints (in theory) about LED lighting.
Not just flicker, but also limited colour temperature spectrum range, too much blue frequency spectrum (with all sorts of worries about that, as regards humans well being), and maybe other things too.

My real complaint (sorry but it is POLITICAL). Is I don't mind the EU encouraging us to use LED lighting. But encourage us by advertising and/or discounts on LEDs and maybe gentle taxation on non-LED lighting.

BUT to just make laws, so that most alternatives to LED lighting are BANNED. Is just draconian.
If you can understand what I mean. It should be OUR choice, not some "invisible", somewhat unelected decision makers in the EU.

I'd prefer to have the option, of using Halogen or even the older tungsten filament, lighting, where applicable.

E.g. for choosing the BEST lighting for any Electronics Lab work area and working lights.

The lack of colour gamut (or however I should describe the potentially limited light spectrum from LED lighting), can mess up colour identification (e.g. resistor colour band codes), and hence I presume, the potential quality of finer electronics work.

Since Brexit has occurred. At least in the UK, it may potentially have different laws. But no real sign of it yet.

[SeanB]

Well, just looked at the light I upgraded with some cheap eBay 10W buck converters ( 12-24VAC/DC in, 3-6V 900mA out) and 4 3W 4000K'ish cheap LED star clusters ( bought 50 as this was around the same price as 20 incl postage) running as 2 series strings of 2. Output flicker is a very tiny oscillation at 1MHz from the buck converter, 10mV on top of 700mV of output. Measuring device is another star LED used as a photodiode, so well matched to the emitter. Bright light this, a lot more light than the 50W halogen lamp that used to be in this Luci Abele desk lamp, and at 10W it runs a lot cooler as well. Hopefully running the chips at slightly lower level will be good for life as well.

[Vtile]

There are all sorts of complaints (in theory) about LED lighting.
Not just flicker, but also limited colour temperature spectrum range, too much blue frequency spectrum (with all sorts of worries about that, as regards humans well being), and maybe other things too.

My real complaint (sorry but it is POLITICAL). Is I don't mind the EU encouraging us to use LED lighting. But encourage us by advertising and/or discounts on LEDs and maybe gentle taxation on non-LED lighting.

BUT to just make laws, so that most alternatives to LED lighting are BANNED. Is just draconian.
If you can understand what I mean. It should be OUR choice, not some "invisible", somewhat unelected decision makers in the EU.

I'd prefer to have the option, of using Halogen or even the older tungsten filament, lighting, where applicable.

E.g. for choosing the BEST lighting for any Electronics Lab work area and working lights.

The lack of colour gamut (or however I should describe the potentially limited light spectrum from LED lighting), can mess up colour identification (e.g. resistor colour band codes), and hence I presume, the potential quality of finer electronics work.

Since Brexit has occurred. At least in the UK, it may potentially have different laws. But no real sign of it yet.

I share a secret. You can get good old tungsten heaters if you buy them with "for industrial use" stamp and they miracularly have usage hours of way above 1000 hours. 

[tooki]

There are all sorts of complaints (in theory) about LED lighting.
Not just flicker, but also limited colour temperature spectrum range, too much blue frequency spectrum (with all sorts of worries about that, as regards humans well being), and maybe other things too.

FWIW, the LED bulbs that have come out in the past year or two are vastly better than what was around even just 5 years ago. The color spectra are hugely improved, to the point that they are almost impossible to distinguish from incandescent.

(I wear fairly thick glasses, and towards the edges, I get a sort of prism effect that breaks up the light into the spectrum. In older LED bulbs, a dot of light broke into distinct bands of red, green, and blue, or yellow and blue. The modern ones have a quite smooth spectrum without noticeable peaks or bands —  just like incandescent. Not scientific, I know, but I don't have a spectrometer at hand. )

[MK14]

I share a secret. You can get good old tungsten heaters if you buy them with "for industrial use" stamp and they miracularly have usage hours of way above 1000 hours. 

Thanks for that. I did not know that there was such a work around, for the issue. I knew that "new old stock", bulbs of various forms, were obtainable on ebay. But did not realize there were (or had been) loop-holes.

Unfortunately I have too much respect for my EU masters, to buy "industrial use", for use at home. 

http://www.dailymail.co.uk/news/article-2193792/Old-fashioned-lightbulbs-banned-EU-directive-sold-traders-loophole-allowing-renamed.html


It is fairly obvious (putting my electronics hat on), that there are various ways the LED lighting can be flicker free (because LEDs are flicker free, from DC or constant current sources. Even high frequency PWM, may be acceptable, if necessary). It just may need a modest increase in the cost of the LED lighting. Given that the electricity savings are huge (compared to tungsten bulbs) and they can potentially last a very long time, such as 10,000 hours.
I can't see why that modest cost increase (to eliminate flicker, and ideally improve the colour gamut spectrum and maybe other improvements, such as blue light minimization). Can't be done.