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I have installed lights in my house. The lights don't appear to flicker to the naked eye. However, when I view them through the video camera on my iPhone, the lights appear to flicker at a very high rate.

Is this bad for my health? Are the lights defective? How can I fix this?

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    The flickering is picked up due to two rates that it didn't sync up with: 1) refresh rate of the camera capturing device 2) refresh rate of the display. If it happens to not be a matching rate of BOTH of these, then you'll see flickering.
    – Nelson
    Sep 29 at 2:52
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    [This is more to do with photography than DIY, so just as a comment] You can get totally flicker-free LEDs, but they're usually specially for video lighting [& expensive]. Many of the rest [domestic, cheap ones] flicker at some multiple of your national mains frequency. Some video cameras have an anti-flicker setting, but for stills you need to try set your exposure time to also be a multiple of your mains frequency, which can be tough from a phone, easy on a real camera.
    – Tetsujin
    Sep 29 at 7:42
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    Different people can see flicker differently. If you can't see it naturally, then forget about it. If you can see it, like me, you're in for a life of pain as you try to find flicker-free lights. Hint, peripheral vision is faster than central vision for seeing flicker. VTAC is a cheap brand of LED lights that I've found most examples of are flicker-free. Often expensive brands are flicker-free, but not always.
    – Neil_UK
    Sep 29 at 10:36
  • What is the mains frequency where you are? How to Remove Light Flicker While Recording Video on iPhone might be helpful. Sep 29 at 18:37
  • If the flickering is a concern while filming, you will need to upgrade to a camera that can be gen-locked to your lighting system.
    – Glen Yates
    Oct 5 at 14:31

5 Answers 5

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LED lights actually flicker very quickly. It only shows up in video, your eyes don't care.

It's fine.

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    It may be, @EyalCohen, that the "don't flicker" lights just so happen to flicker at the same speed as the shutter of your camera. They do flicker. If you have/know someone who has a camera with a manual shutter speed control, set the shutter speed to about 1/1000 second and take some pictures of the lights. You'll get pics with some lights on, some off, even though you and your phone can't see them flicker. I've done this taking pics of scoreboards at gymnastics meets - hard to read the scoreboard with ~20% of the lights on...
    – FreeMan
    Sep 28 at 18:33
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    @EyalCohen if "flicker-free" onvideo is important to you you'll need different lights or a different camera shutter speed. If you think it's bad then why ask?
    – Tiger Guy
    Sep 28 at 23:31
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    @ThaRobster: It's entirely possible to make LED lights that don't flicker. Very often they do, because many of the efficient/cheap ways of driving them do make them flicker - especially if there's any sort of dimming (and, as many have said, it largely doesn't matter if they do flicker). But there's nothing inherent about LEDs that means they have to flicker.
    – psmears
    Sep 29 at 9:44
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    Adjusting the true intensity of an LED is difficult; they can be very sensitive to even minor changes in voltage. Adjusting the apparent intensity through flickering is much easier.
    – Arthur
    Sep 30 at 11:36
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    @Arthur controlling the current instead of the voltage is not difficult.
    – user253751
    Sep 30 at 18:15
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The majority of artificial light sources flicker, but they do so with different amplitudes and frequencies.

If you have lights powered by direct current (DC) from a battery:

  • An incandescent bulb will not flicker.
  • An LED driven directly or with a resistor will not flicker. But an LED driven with a buck/boost DC-to-DC converter might flicker, possibly at a high frequency.
  • Fluorescent lamps are usually not powered by DC.

If you have lights powered by DC that was converted from AC, they might flicker a little bit due to ripples in the power conversion. Simple converters based on a transformer and filter might flicker at 100 or 120 Hz (twice the power frequency). Better converters based on SMPS might have essentially invisible flicker in the tens of kilohertz.

If you have lights powered by alternating current:

  • An incandescent bulb will flicker a tiny bit at 100 or 120 Hz. The thermal mass of the tungsten will keep the light output pretty steady, but there are still subtle fluctuations of heating and cooling.
  • An LED hooked up directly to power will flicker strongly at 100 or 120 Hz. Cheap Christmas lights, which are strings of LEDs, tend to be like this.
  • Other LED bulbs have AC-to-DC conversion circuitry, possibly with inductors and capacitors to smooth out the power, and possibly use SMPS high-frequency conversion.
  • Old, big fluorescent lamps will flicker moderately at 100 or 120 Hz. The color may shift between orange-ish and blue-ish during each cycle.
  • New compact fluorescent lamps (CFLs) have onboard power converters that will produce invisible flicker in the tens of kilohertz.

CRT televisions/monitors are a great example of strong flicker. You can use them to test how your eyes react, and easily adjust the frequency through video output settings. For example, in my peripheral vision I can see flicker at 50 Hz but not at 60 Hz.

If the flicker frequency is too low (let's say below 50 Hz), it could potentially cause eye strain, fatigue, and disorientation.

Moderate flicker frequencies (say 100 Hz) are generally fine, but can produce slightly annoying artifacts when the light source moves or when objects move. For example, moving your hand under a flickering light source can produce ghost copies of the hand. For example, a flickering car tail light can produce many copies of the light against a dark background.

Another consideration is that in machine shops with spinning equipment, a flickering light source can produce the aliasing illusion that a fast-spinning machine is stopped or going slowly; this can be a safety hazard.

And finally, if the flicker causes visible problems in the photos or videos that you take, then by definition the flicker is bad for that particular use case.

Overall, non-flickering light sources are the most natural to our eyes and cameras, but moderate flicker frequencies (around 100 Hz) can be tolerated by our eyes very well.

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  • This account isn't linked to your profile.
    – Mazura
    Sep 29 at 0:55
  • @Mazura Maybe you're referring to how I hid communities where I haven't earned a significant number of reputation points above the 101 baseline
    – Nayuki
    Sep 29 at 5:54
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    Actually, a lot of LED's are driven by a pulsed source, with the overall brightness then controlled by the duty cycle of the signal, so its's not just those driven by the mains.
    – MikeB
    Sep 29 at 10:34
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If you can't see it, then it does not matter. But some people are more sensitive to flicker than others.

With LEDs, the amount of flicker depends on the quality of the LED driver circuit. If you care enough to change the lamps, try better quality ones from a reputable manufacturer.

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    It's not just LEDs that exhibit flicker. Old CRT computer monitors used to refresh slow enough that I could see them flicker, but nobody else could. I'd bump the refresh rate up on mine as high as the video card would support, but everyone else thought I was crazy.
    – FreeMan
    Sep 28 at 18:30
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    @FreeMan I can also see it. 60Hz was the minimum I needed, but some people wouldn't see it even at 50Hz. Also, your peripheral vision is more sensitive to flickering than directly looking at it.
    – Nelson
    Sep 29 at 2:54
  • The higher the quality the less flicker right?
    – Eyal Cohen
    Sep 29 at 6:05
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    @EyalCohen yes ... if by "better quality" you mean flickers less! A flickering lamp usually means they under-sized the capacitors to save money.
    – Simon B
    Sep 29 at 8:21
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First, look at the light from the corner of the eye. It will be easier to catch some flicker, peripheral vision is more responsive than foveal.

If you don't see any flicker, lights are good enough for you. You might still want to replace those bulbs to take better videos inside, but it isn't a must-have. Guests that are more sensitive to flicker could notice it though.

If you see some flicker, even if just slightly, I suggest replacing the light bulbs. Flicker won't do any noteworthy damage by itself. But it will tire you and watching that can be stressful, so it may do some damage indirectly. Fairly fast and cheap bulb replacement is a very cost and time efficient improvement.

The only reasonable thing you can do here is replacing the bulb if needed. You shouldn't try to fix bulb. The main problem is that cheapo bulb skimped on capacitors and so there is not enough smoothing of the AC sine wave towards something resembling constant DC. You get voltage and current variation, meaning brightness changes. It IS possible to open up the LED and replace electronics. But this operation will only fix amount of flicker and bulb efficiency at the cost of brightness - colors will remain the typical poor 80-ish CRI of cheap bulbs. I consider this a waste of effort over simply buying a better bulb; if you really want to do a lot of DIY here you can buy OEM LED chips and assemble the whole thingy yourself.

All AC LED bulbs I saw flicker. Most of them flicker at 20 kHz, give or take few 10s kHz. You won't see that with eye or on a typical home camera, but you can see it on a high-speed camera. Cheap bulbs flicker at lower frequencies, those are noticeable by eye or normal cameras. DC LEDs either flicker or not.

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    The other thing that will help detect flicker besides using your peripheral vision is to turn off all other artificial light sources (and maybe do this at night or in a darkened room), and then wave an object (e.g. your finger) back and forth in front of the light. You should be able to see a strobe effect of the object's movement. Sep 29 at 21:15
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The is-this-bad-for-health part of the question has not been answered yet. You would have to turn to scientific literature. Following are two links to papers and while I didn't read them fully, the abstracts imply that there can be negative effects on health like eye strain and headaches.

Potential Biological and Ecological Effects of Flickering Artificial Light

Light Emitting Diode Lighting Flicker, its Impact on Health and the Need to Minimise it

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  • That's what I was looking for. IDK why some people unliked you. but this is the answser i was looking for.
    – Eyal Cohen
    Oct 4 at 9:39

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