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Comment by mrb | Hacker News Reader

Lifetime isn't even my #1 concern with LED bulbs. It's strobing/flickering.

I film all the LED bulbs I buy in slow motion at 240 fps with an Android phone, and play the movie back on a PC with mplayer using the dot(".") key to move frame by frame. Here is a shot I made comparing 2 brands of LED bulbs: https://youtu.be/QbenId_F2RQ (Edit: yeah you don't have to transfer to a PC, just playing back in slow motion on the phone will still show the effect quite well.)

It's amazing how I find this way that most (but not all!) of LED bulbs flicker with a strobe effect at 120 Hz (frames alternate between bright and dim) because they have crappy power supply designs that fail to smooth the A/C voltage. As a result they flash one time during the positive phase and one time during the negative phase of the 60 Hz A/C mains frequency.

I find this unacceptable. Although not too noticeable in normal conditions, a 120 Hz strobing light is definitely noticeable when your eyes move or track an object illuminated by the bulb.

In my experience, Philips lightbulbs are one of the few brands that don't have this flaw because they take care of converting AC to a stable DC voltage internally. In fact they are advertised as such: https://www.amazon.com/dp/B07CFRCGKC "COMFORTABLE LIGHT: Our products meet strict test criteria including flicker, strobe, glare and color rendition to ensure they meet EyeComfort requirements"

View on HN

LED flicker could prove harmful or fatal if you work with anything that rotates or reciprocates.

The rotating / reciprocating mass may appear stationary at some RPM.

Just a reminder to only ever use incandescent or halogen lights around machinery you can touch while in operation: drills, lathes, mills, slotting machines, etc.

Just how likely is this to happen though, it would have to be the only light source and be flickering with exactly the same frequency as the machinery is traveling at (which i assume for most devices varies a lot).

Not saying it can't happen but it does seem stupidly hard to achieve.

It doesn't have to be going the exact same speed, a multiple would do the trick too. It can also be dangerous if it's close to the same rate since it can then look like it's going slower even if not stopped.

Or the rotating / reciprocating object may appear to be rotating / reciprocating slowly in the opposite direction.

Even after 20 years in the metal fabrication industry that scenario still spooks me.

This is uncommon but not rare. Have you ever seen wheel blur or other artifacting of such? It's very easy to make happen artificially under controlled conditions which means it can't be that hard to happen accidentally.

Edited to add: Have you ever heard of a timing light for an engine? This works exactly the way you are describing.

The effect might not be rare but getting hurt by it is incredibly rare. Machines produce noise and vibration. Nobody is going to be fooled and try to pull a moving part out of a lathe because of some LED lighting except in the most exceptional or bizarre circumstances.

Nobody? That is a high bar. Mechanics tend to be pretty cluey, but for the effort of getting proper lighting why nobody should be taking that sort of risk. Sight is one of those fundamental lets-feed-in-useful-information sensors for keeping situations safe.

Most people spec'ing out machine shops are not experts in lighting other than more = better. This is a really, really low risk we're talking about. Like basically the stars have to align for someone to get hurt.

I started to write a lengthy rebuttal, but decided to go with something more concise.

Never underestimate the ability of machinery to rapidly render you dead.

Never underestimate the ability of otherwise intelligent people to intentionally disable safeguards, or guninely make mistakes.

No, it simply isn't that rare. You haven't been around wood shops and machinery much if you think that.

Are there any statistics on this? That seems like the obvious way to settle this issue.

So far, the discussion sounds like it's a theoretical possibility. If it's a real possibility, then it's something that should have happened a number of times.

Machine shops are very loud (plus you'd be wearing ear protection) and a lathe/mill that vibrates noticeably is either broken or incapable of performing the very task its designed for.

Timing lights for engines work this way for clarity: The distributor on an engine has a spinning rotor and a number of points (one for each sparkplug) on the outside the circle the rotor forms while spinning are a series of contacts across which electricity jumps to send voltage to the spark plug.

The timing light is then pointed at the flywheel on an engine, which has numbers or marks stamped into it. Each time the spark plug fires the timing light (which is hooked into that same current via induction) lights up for a brief amount of time to show at what timing offset the engine is currently at. (this all happens at hundreds of rpms a minute).

so I'm not sure it's the same

I would imagine there's a higher-than-average chance of this because most AC motors are definitely syncronized with the 60hz (or 50hz) AC source. There's a chance the lights might also derive from this.

> There's a chance the lights might also derive from this.

If the light is flickering it's absolutely guaranteed that it's derived from this.

But it's hard to imagine a lightbulb that emits a short enough pulse of light to make something look stopped. Even an absolute garbage one-way rectifier will be emitting light more than a quarter of the time. That can make a tool look odd, but it won't make it look still.

If the light is flickering it's absolutely guaranteed that it's derived from this.

Not necessarily. If it's a 50/60 or 100/120 Hz flicker then yes, but LED lights with a cheap switching power supply might still flicker at the switching frequency, which could be say 400Hz or something.

You have to be intentionally wasting money to put in a transformer big enough to handle 400Hz, and once you get into the lots of KHz where a supply like that is happy I think your "please don't explode" capacitor on the transformer is enough to prevent flicker.

You would also have to ignore or miss any other signs of very fast rotation, such as noise or air movement or the power switch being on.

It's easy to miss those signs too. It's common to have earmuffs and sometimes a dust mask on when using power tools, and power switches often don't clearly indicate state. Many start/stop control boxes don't have any visual indication of state at all.

Someone might hear the noise and feel the vibration but think something is broken inside because the drill isn't rotating. I'm not sure exactly how that would lead to an accident but it might.

I can also imagine the sound and moving air being masked by safety gear making it even more likely to note the movement.

It's not true that it has to be the only light source. All of the light sources have to be the same type and on the same circuit, which is fairly common.

Many AC motors are synchronized to the frequency of the power line, by the same principal that turbines in the power grid are. So 60hz AC often means 30hz = 1800 rpm motor, and 59.8hz AC means 29.9hz motor. So if you have LEDs with a half bridge rectifier and your machinery is 180 degree rotationally symmetric, it will appear to not be moving, even if the line frequency fluctuates.

Pretty common, about as common as the wagon wheel effect in 24fps film movies. In just the same way, the item can appear to stop, run slow, or run backwards, just as with film. No it does not have to be the only light source, just the nearest one to the machinery.

Fluorescent tubes are most noticeable, LEDs a little less. Tungsten or Halogen are the only sensible option for workpiece illumination.

I believe halogen is also tungsten.

It is. Just running at higher temperature. They tend to be marketed as something separate and distinct though.

Or, of course, just use a LED that properly smooths out the DC. It's not hard to do, and a quality LED manufacturer should get this right. The only excuse for flickering is a cheap LED that cuts cost for circuitry.

Oh I agree, but a surprising number of LED bulbs have some degree of flicker, even from those makes you might expect to do better. A purpose made work lamp should get it right though. Hopefully. Maybe.

For my hobby stuff, I just bought a couple of spare halogens that should see me out.

> which i assume for most devices varies a lot

Most will flicker at a multiply of the power line frequency (60 or 50 Hz depending where you live).

It's so common, that most digital cameras have a setting to set the power line frequency, so they can reduce the flickering in the footage.

Incidentally - many alternating current engines are also working with multiples of the powerline frequency, because it's easier that way.

Multiple light source of the same general characteristic (don't even have to be the same type of bulb) may produce this result.

The rotation frequency would have to be close to a relatively simple multiple (or fraction) of AC frequency but the way electric motors are contstructed if the piece is directly connected to a motor it is very likely it is true.

Yeah, please don't rely on your eye sight to tell you if a tool is operating. Every time a tool is running you should know it is because you started it to a specific purpose.

Before you start a tool you should act out your planned motion. Then start the tool and only perform this motion. If something changes and you cannot complete the motion, stop the tool immediately. Following this and a few other safety tips I've operated power tools for years without incident and I'm legally blind.

> stop the tool immediately

Okay, but, say you've configured the tool wrong and now it's destroying your work. You stop the tool. How soon is it safe to grab your work away from the work surface—i.e. when will it go from "it's too dangerous, let it keep destroying the work" to "it's now slow enough to pull the work off of the tool while it's still—slowly—running, to save the work from further damage"? That's a thing you have to figure out with your eyes (and ears).

such devices are usually not allowed in those cases. (speaking of DIN EN 12464-1)

Oh, WOW!, I never thought of that! Thank you for this information. I thought I am very careful but it never occured to me this could be a problem.

So I went of and did a tiny bit of research. Turns out there are LED work lamps designed specifically for lathes etc.

So, evidently, I may have over stated my initial claim about only using incandescent lights.

Still, it’s something to me conscious of.

I only buy Philips bulbs for this very reason, or from brands that advertise being flicker-free. With iphones, slow motion mode also makes the flicker very visible without the need to transfer to a PC.

Visible light impulses influence brain wave patterns (e.g. [1]), and it might not be beneficial to look at pulsed light with a frequency that is not well researched.

Same thing with screens, most LEDs are dimmed with pulse width modulation [2], so they flicker at most brightness levels except the very brightest one. Some iPhone X users claim they get a headache when looking at the phone at the lowest brightness setting (OLED is even worse in that regard than LED, IIRC).

1: https://clinicaltrials.gov/ct2/show/NCT03657745 2: https://www.eetimes.com/document.asp?doc_id=1281013

I had a small bag of Chinese position light LED T10 lamps for my car my dad had given me. I would change them every three to five months because the LEDs would burn out. Getting sick of sticking my hand in narrow spaces to replace the lamps, I ordered two Philips Xtreme Vision 4000K T10 LED lights. They've beeen running flawlessly more than a year now.

Very good points here, I would add that 99% of the monitors are also flickering when you dim their ligth. This is why i started using the iris[1] app on my laptop. Keeping the brightness at 100% in the hardware settings will eliminate the flicker, then iris dims the lights from your graphic card. I can work without eye oain thanks to this method. - [1] https://iristech.co

Oh, I had been looking for something like this for the desktop, thanks for mentioning it!

On iOS there’s a setting buried deeply in accessibility settings, I think it’s called white point correction.

>Some iPhone X users claim they get a headache when looking at the phone at the lowest brightness setting (OLED is even worse in that regard than LED, IIRC).

And on iPhone XS this is even worst. I wonder if there are any solution to PWM problem.

We need IEEE PAR1789 bulbs! The department of energy has a great presentation on LED flicker and this IEEE standard for better bulbs, https://www.energy.gov/sites/prod/files/2015/05/f22/miller%2...

What I've found to help weed out the worst of the worst is to only buy dimmable versions of the bulbs. They cost more but because they have to support dimming they're almost required to have a better power supply to handle the usual triac based control that most dimmers have.

Not sure this always holds.

The worst bulbs I've personally seen for flicker were dimmable ones.

The non-dimmable variant from the same range had no noticable flicker.

Price paid also seems to be no indicator of quality – I've had premium LED bulbs from major makes, bought from a reputable wholesaler, that have died after 6 months within days of each other.

I've had cheap no-name imports that have lasted years and had no flicker.

Yes, the dimmable has been the worst for me so far, they just make them flicker more to give less light.

Confirmed. Have dimmable at work and home and they flicker like crazy.

A lot of "dimmable" LEDs are actually shifting the flicker pattern to dim the light (shorter on phases). This is for LEDs where the user dims per remote control. OP was talking about the older "legacy" dimming, where you have a wall-mounted knob that reduces the current. Works well with incandescent bulbs. But only few LEDs support this. If they do, their internal power converter likely won't flicker, because of their more thought-out converter?

However, there are also LEDs that support legacy dimming, but again translate less current into different flicker patterns...

I've been trying to switch to all-LED in a home with lots of legacy dimmers and it's been painful. Even on circuits where I've replaced older dimmers with new Lutron CFL/LED dimmers, I get flicker.

In other places I don't have dimmers but have low-voltage (12V) cans. Lots of flicker issues there too, presumably due to the 120->12V transformer at the can.

And then I have a light fixture that's both dimmed and a custom 12V setup. I've given up on finding a working dimmer/LED bulb (MR16 GU5.3) there. Probably need new 12V transformers?

I'm really happy to see you post this. Everyone else I've brought it up too just says I'm crazy. I might be crazy but not about the damn flickering/strobe.

Especially when my dog bounces around it looks like she is in a strobe light. I did a couple of videos of it just to "prove" it in some fashion.

https://www.youtube.com/watch?v=DddB_0QrV_8

You’re definitely not crazy. HN also had a big discussion about it two months ago in this¹ thread as well.

――――――

¹ — https://news.ycombinator.com/item?id=18644590

The people who are crazy enough to think they can change the world are the ones who do.

I use a salt shaker and pour salt onto a plate - if I can make out single falling grain of salt on the way to the plate, I know this light source is not healthy for humans.

Hang on, how does that work?

A metal working friend told me recently that in Australia we're not meant / allowed to use fluorescent lights above lathes, as the flicker can disguise movement.

This is slightly worrying.

Yeah gas discharge lamps (CFL, neons, halides) will flicker at twice the mains' frequency on a single-phase circuit, makes it very dangerous to use them as e.g. factory lighting. You can mitigate that by using 3-phase power supplies, high-frequency controller, or by supplementing the basic lighting with incandescent bulbs around machinery.

The stroboscopic effect is really fun right until you're in a place with lots of moving parts at a multiple of the strobe frequency.

OTOH it's also used to fine-tune engine timing and such: set a stroboscope at a fraction of the frequency you want, the engine is properly tuned when everything looks completely stopped. Makes it very easy to notice mistiming.

Some turntables include a strobing light and rings of dots around the edge for different speeds. If it's spinning at the correct speed the corresponding dots will stand still.

Absolutely - the way he described it sounded like a horrendous accident waiting to happen, especially for smaller / home shops where the operator may not be aware of the problem. He was under the expectation that LEDs solved this problem, though he is using drop-in LED tubes that may have some better persistence through the off-cycles.

I do some occasional wood-turning, but usually augmented with ambient daylight - along with the dubious safety advantage of having a very noisy electric motor.

Plus I'm old enough to have used a timing light hanging off a distributor on my first car. Try explaining that to the kids of today. ; )

A friend of my mother's lost half a finger to a strobing light and a circular saw. It does happen!

Modern CFL drivers have frequencies in the tens of kilohertz.

The flicker is a thing from the past (or should be).

Shaking a hand with fingers spread out somehow works to spot flicker. If the light source flickers, you see oddly sharp finger positions in the air. It's not the most sensitive or easy to interpret method.

The John Cena method?

I remember doing this with CRTs

I calculated the airspeed of a rubber band this way once! My coworker shot a rubber band in my direction. I noticed three “shadows” of the rubber band as it passed by the CRT.

The CRT was a 17” running at 60hz. The rubber band sailed past in the span of about 2 screen refreshes, so it traveled that distance in 2/60 of a second. Distance was easy to calculate by the Pythagorean theorem or by holding a ruler to the screen, I forget which.

I completely agree, flicker has been the most distracting part of switching to LEDs, for me.

Here are two good sites that posted graphs of light intensity over time for a bunch of different bulbs: http://www.ledbenchmark.com/ http://sle.se/michael/led/ (Swedish)

Unfortunately, they both stopped updating around 2015. Anyone know of similar sources for more recent bulbs?

In the huge HN thread here¹, yeutterg mentioned² their Bedtime Bulb:

> “I am on a mission to make lighting healthy. That's why I made Bedtime Bulb: https://bedtimebulb.com/ It has the lowest flicker I've ever seen in a bulb form factor—even less than those claiming to be "flicker-free."”

In addition to that, a few other database sites that test for flicker were mentioned here³.

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¹ — https://news.ycombinator.com/item?id=18644590

² — https://news.ycombinator.com/item?id=18650624

³ — https://news.ycombinator.com/item?id=18646409

I've tested a bunch of bulbs for flicker with a handheld flicker meter and with a photodiode connected to an oscilloscope. It's funny that some of the bulbs out there claiming to be "healthy" have terrible flicker. One product from Soraa was flickering at over 50%, almost as bad as the cheapest/worst LED bulbs you can buy.

I don't have a database, but I can say that most (but not all) filament designs are terrible for flicker--ours is an exception. Philips products seem to have gotten worse in quality over time, probably to remain competitive, but they are better than the worst. Ikea's stuff is pretty good overall. I don't have a consistent recommendation for low-flicker general lighting right now, as every brand has good and bad products.

Thanks to GP for the links, I completely missed that previous thread!

And, yeah, I tried that Soraa healthy bulb, and it was shockingly bad, given how it was advertised. Even the regular Soraa bulbs were disappointingly flickery, though less so. Also, just looking at the pattern it makes on my phone's rolling shutter, the wave is quite saw-toothed, and I wonder if that makes it worse? I have some Ikea candelabra bulbs which were always pleasant, and I was surprised to see they also left quite a visible flicker pattern on my phone, though much more sinusoidal/smoother.

It's a shame about the flicker in the Soraa bulbs, since the colors really did seem nice.

The Soraa bulb looked pretty sinusoidal on my scope when I tested it briefly. But it's a lot of flicker regardless.

What's interesting is that the bulb seems to have a nice build quality (from the outside, I didn't open it) and is quite heavy. I suspect they are putting a BIG heatsink in there, as violet pump phosphors tend to degrade quickly.

The other thing that irks me about this product is the "zero blue" messaging. Yes, I can confirm the spectrum looks like what they are advertising, with a peak around 415nm, almost nothing between 440-490nm, and then all the rest of the colors from green to red.

But, green light is just as bad as blue for sleep! The ipRGCs are sensitive to both blue and green (up to around 600nm) This bulb has a lot of green, more than a lot of other light sources. It also has a very unpleasant greenish color (IMO) and low-ish CRI, around 78 on the bulb I tested.

Is it better than a normal 600lm bulb for sleep? Yes. Is it novel? Yes. Is it good in practice? I don't think so.

That's right, the Soraa Healthy was very green! So, even without the flicker, the fact that it makes everybody look like undead zombies would be reason enough to disqualify it as a bedroom night light.

Haha, totally agree! If you are still in the market for a low-blue, low-flicker solution, may I humbly suggest a look at my product, Bedtime Bulb [0]? I know I basically bashed the Soraa product here, but not without technical justification.

[0] https://bedtimebulb.com/

> flickering at over 50%

what does that mean? Duty cycle is 50%, frequency at something Hz? Not being snarky - curious whether there is some kind of standard that your tool compares against.

A duty cycle 50% (or any percent really) isn't bad in itself, it's the frequency that is the culprit. Too low PWM freq and you'll notice it.

When I refer to % flicker, I am talking about the modulation % as defined by IEEE 1789-2015 and some documentation from the Illuminating Engineering Society [0][1]. More correctly, invisible flashing is known as the stroboscopic effect or phantom array effect.

Two factors are often used to describe flicker for lighting:

- Modulation %, a.k.a. % Flicker [The height or modulation of the waveform, formula is 100% * (A - B) / (A + B)]

- Frequency [self-explanatory]

Flicker Index is also used (refer to [1] page 7 for more info) but rarely.

Duty cycle is not considered relevant, as you mentioned.

Some tools designed to measure lighting, such as my UPRtek CV600 [2], spit out % flicker, frequency, and flicker index, in addition to a bunch of spectrophotometry metrics. It's also pretty easy to calculate the modulation % with an oscilloscope and photodiode, it's just Vp-p / Vmax.

IEEE 1789 [0][1] roughly says that the higher the flicker frequency, the more acceptable it is to have a high modulation %. If you look at the graphic on [1] page 18, you can see this relationship. The white area is considered unsafe, the yellow area is "low-risk", and the green area is "safe." I don't 100% agree with this personally, as most incandescent lighting, with around 6-11% flicker at 100-120 Hz, would fall into the unsafe or low-risk category. But the Soraa product is definitely in the unsafe category.

For reference, I plotted my product (Bedtime Bulb) against an incandescent A19, Lighting Science's Goodnight A19, and Soraa's Healthy A19 on an IEEE 1789 graphic [3] with a Python tool I'm developing, Beautiful Flicker [4]. You can see that this incandescent, measured around 10%, is on the border between unsafe and low-risk by this standard.

Hope this helps!

[0] IEEE 1789: A new standard for evaluating flickering LEDs?: https://www.dial.de/en/blog/article/ieee-1789-a-new-standard...

[1] Flicker: Understanding the New Recommended Practice (PDF) https://www.energy.gov/sites/prod/files/2015/05/f22/miller%2...

[2] UPRtek CV600 https://www.uprtek.com/en/product/SPECTRAL-COLOR-METER/CV600...

[3] IEEE 1789 Graphic Comparing 4 Light Sources https://github.com/yeutterg/beautiful-flicker/blob/master/ou...

[4] Beautiful Flicker https://github.com/yeutterg/beautiful-flicker

I don't think I could have wished for a better answer, thank you. Love it when a new area opens up to me like that! While I'm not active within lighting per se, some of our customers are, and this will help me understand the complexities of their products better. So, thank you, it does help!

So glad this was useful! Please let me know if there's anything else I can help with lighting-related. I'm super easy to find.

This concerns me. About a year ago I went onto a website and ordered 56 led bulbs for my entire house and thought I got a fairly good deal. They worked seemingly well but my eyes always felt strained when under them. Just took my iphone and can definitely see the flicker with slow motion. And when I look at items as I move my head across the room I feel like I can see it as you say and never really knew what I was experiencing before. As someone who always talks about having sensitive eyes to light I am definitely not happy about this and am now thinking about buying flicker free bulbs. Thanks for sharing.

Next time, a good resource is https://ledstrain.org/. I found it here in HN and is quite informative for makign decisions on what to buy.

I usually just move my phone really close to the lightbulb and watch the live camera view. At a certain distance/angle you can usually see the flicker as banding across the screen.

I saw a test in a Swedish newspaper lately that showed IKEA's cheapest lightbulbs as one of the less flickery ones in the test. IKEA art.nr 303.887.64. So much for the price to guide you.

Bought an IKEA led lightbulb for €3 and the packaging says it should last 15000 hours. Not bad really.

LED lights are alright. Lots of people think that everything used to be better but my memory is too good to fall for that trap.

I can spot a Cadillac or GMC vehicle on the road a mile behind it from the flicker of the taillights. It's terrible.

Why do they flicker? Are they AC powered?

You can dim LEDs by turning them on and off really fast using a process known as pulse width modulation (PWM). Ideally for something like brake lights you would use a constant current driver to control the light level to prevent flickering. I don't know why GM is using PWM, but I'm guessing they just use a cheap control circuit. I really hate their LED tail lights. Just moving your eyes from side to side is enough to easily see the flashing.

Also, due to leakage for large LEDs they are more efficient at higher current. That means that for a given power, you're better off driving them at a higher current for a shorter duration. You can increase the effective luminance without violating the power spec.

Agreed. Most car manufacturers' LEDs flicker (just look at any slow-motion video, such as those on Top Gear or The Grand Tour), but GM's are at a much lower frequency that is visible if the vehicle is in motion, or you are in motion.

I always wondered if anyone ever tried to encode information into the flicker pattern of LED tail lights. I can think of a lot of uses, good and bad.

Some people are talking about using LiFi or high-speed IR communication for vehicle to vehicle communication. Seems like a great idea, but you can do it at a much higher frequency than what GM is doing today, so it's not distracting to humans.

Cheap brands generally use some form of capacitive dropper scheme. These result in the 120/100Hz flickering but is cheap to produce as very little components are needed (X2 class capacitor, maybe some current limiting resistor(s) and a discharge resistor, bridge rectifier, or even skip the rectifier altogether). They are not to be used with a dimmer. Some info on them [1]

The switch-mode power supplies in proper lamps get the stuff done way better and there will be no noticeable flicker. Maybe in the order of several kHz in ripple which you cannot see.

Also; cheap off brands (looking at you china) sometimes have caps rated at 250V which is far from the peak mains rate of about 320V (in 220/230V countries).

[1] https://www.powerelectronictips.com/whats-stuff-capacitive-p...

I have electric heating and in the winter there is no energy benefit at all from LED bulbs. I want my incandescents back. They really feel comfortable in a way I can't explain.

They really do. I placed an incandescent on a floor lamp to use it for reading, and it's now the most pleasant light on my house by far. But it gives me anxiety to leave it on for a long period of time because I know it's a huge waste of energy. The second best are my Phillips SceneSwitches, which I really love but don't come in 100w.

I just went and tried to find a bright (1000-1500 lumens) Philips LED bulb with a cool temperature (3500-4500)... but it seems every Philips LED bulb is "warm white"* :/ That's fine for a living room, but not what I want in my home office, kitchen or bathroom.

* at least in the UK

I'm surprised no one has mentioned hte rise of flickering LEDs on cars - though I think in this case it's caused by PWM dimming.

I mean, it looks absolutely fine as long as the light source and viewer are both static - just a shame vehicles tend to be moving :(

I don't get why DLR LEDs needs PWM at all. It 100% can be done without, even with smooth light distribution.

Perhaps dimmable LED bulbs would be better in that regard? The LED dimmers on the market use a very high rate PWM (afaik) to prevent/minimize flickering at low brightness. I would guess that the dimmable bulbs are designed to work well with intermittent power and so wouldn't have the same problem.

Of course it's still hit or miss, compatibility between bulbs and dimmers seems to be very hard to judge without testing these days.

The bulb they link are listed as dimmable (flicker-free silent dimming) aside from the part they quoted.

In my experience, dimmable bulbs are no better. Most of them still suffer from the 120 Hz strobing effect. That's because even though they might PWM at 1-10 kHz to control the dimming function, when A/C voltage crosses zero, the "on" state of the PWM can still be a lot dimmer than the "on" state during the A/C voltage peak.

I would think a good LED would need something like a full wave rectifier with a good smoothing circuit to minimize flicker. I bet a lot of the bulbs on the market cheap out on the electronics though.

Dimmable LEDs are not automatically flicker-free. My father had very cheap dimmable ones, and I complained at every visit about the strobe effect until he bought flicker-free ones.

Most dimmers work via pulse width modulation [1], i.e. the power supply is switched on/off in a different interval (more off time means lower brightness). A true flicker-free dimmed LED has to be dimmed in an analog way (probably only feasible for "dumb" light bulbs). PWM of 20kHz or something might also work, but who knows what that does to brain waves.

1: https://www.waveformlighting.com/film-photography/an-introdu...

I can't find the source right now, but I read that the fastest cells in the visual pathway can respond at a bit under 500Hz. Part of the reason the ieee suggests a minimum PWM frequency of 3000Hz is, for signal processing reasons I don't fully understand, that's the highest frequency the brain could likely detect, given 500Hz "sampling hardware."

You might still get strobe effects where your 500hz sensing nerves eg get a 400hz signal from a 20khz source.

My oven has a high / low switch for the LED lights and I can't have it on low because the strobe/flicker drives me nuts.

Have to mention this¹ big HN thread from 2 months ago with lots of discussion about that exact issue.

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¹ — https://news.ycombinator.com/item?id=18644590

I tried this with my office lamps and saw the flickering so I bought the Philips bulbs you linked to. They just arrived and I filmed them but they also show the flickering when filmed on an iPhone in slow-mo mode.

Do I need to buy a specific model of Philips bulbs? Or is my Ikea lamp the culprit now? I paid a ton of money for a certified flicker free monitor so I'm very keen on making sure the lamps are flicker free as well.

I noticed the same thing when I was playing the guitar. The constant flickering combined with a vibrating string at a high frequency produces a nice looking effect [1], which can be observed with a naked eye (unlike the one in the video).

[1] https://www.youtube.com/watch?v=ttgLyWFINJI

Interesting, I used to be very bothered by computer CRT monitors set at 60hz refresh and bright backgrounds. I'd go into the Windows control panel (most often) and increase it as far as it would go at the given resolution.

Through trial and error I found that 72hz was acceptable/ok and 90hz and above was great. Other folks generally didn't notice, but sometimes could if I showed them to look sideways etc. This must explain why I've never knowingly been bothered by 120hz LED flicker, it is below my ability to consciously notice.

Curious, I took a look at several bulbs, with the mobile at 240fps trick described elsewhere. A new Feit dimmable, new Ecosmart non, a several year old Ikea, and a no-name CFL. All showed flicker except the CFL. All the LEDs flickered, but the amplitude was larger on the ecosmart. Feit and Ikea had a small amplitude.

Perhaps they are putting half the LEDs out of phase to get the smaller amplitude, or they should?

Small correction, the CFL did have some flicker, just small enough I didn't notice on first look.

Have you tried this with incandescent bulbs? They flicker at 120Hz too... since they are P=I^2R and driven directly from 60Hz lines. I don't know the amplitude variation that bothers you, but then I don't mind LED bulbs.

Of course it's not the LEDs that do this but the cheap AC-DC conversion bridge rectifier.

Yeah, but because incandescent bulb filament's retains enough heat to continue to glow between peaks, their flickering is almost negligible - especially compared to poorly designed LED and CF bulbs.

Philips has some solid products. Our old television used to be Philips and it lasted a full decade and a half - we only got rid of it to get an LED TV. Most of our light bulbs have been Philips all my life and they have generally lasted a good while better than other brands we have used.

Yeah I can immediately tell when an area is illuminated by LED lights when I spot the strobing/flickering as I move my eyes and the saccade reveals the slow frequency of the light dispersal (or however it would be worded). It's super jarring and can be a bit disorienting.

On an iPhone - at least the 6S I have - you don’t even need to record a video. Just switching to slow motion in the camera app will instantly show you flicker in the live preview, I assume because it’s interpolating frames from the 120hz input.

You say "don't have this problem", but given sufficiently unstable mains input, the Philips bulbs too will do this.

Source: I just had a problem with a malfunctioning light switch (not even a dimming switch, a plain two-state switch) wherein sometimes it would poorly complete the circuit, and one bulb out of the four on the circuit would start oscillating on and off. (If you removed the one bulb, another would start. If you plugged the first bulb back in, in the original slot or another, it would happen to the first bulb only.)

Never even thought about this problem, thanks for bringing it up

I was in a hotel room a while ago which had some seriously flickering LED lights, just everywhere; moving around you could definitely see it. Wasn't pleasant.

+1 for Philips bulbs.

Lights is something that I used to cheap out on but no more. Not buying Philips bulbs is definitely 'penny wise, pound foolish'.

Also, Philips Hue!

I bought some LED string lights for my bedroom because they were cheap. They turned out to be incredibly annoying due to the 60Hz flickering. Staring at them, it wasn't noticeable but the moment you moved your head or moved something quickly you could see the strobe effect. I trashed them and bought some incandescent lights.

Ah! I'm glad someone found the same thing as I did regarding Phillips bulbs. Here's my old post: https://news.ycombinator.com/item?id=18645237

My Philips Hue bulbs visibly flicker when they are dimmed, but not when they are at full brightness. I never had that problem with the old style bulbs. I wonder if that could be fixed with a firmware update?

Theoretically, they could, but I don't think Philips really has a financial incentive to update anything that "already works"

Yes, I also have the flickering issue with some LEDs, and I can confirm that (to my eye) the philips LEDs I bought do not flicker. I also have a few OSRAM LEDs that don't flicker.

Our WeWork has them in the kitchens - I feel like I'm drunk whenever I am in there!

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