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