Wikipedia:Reference desk/Archives/Science/2025 July 27

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July 27

Fade when turning lights off

I've noticed that when I turn room lights (LEDs) off, there is a fade to blackness. Are the LED lights fading or is it something to do with my eyes, such as persistence of vision? ―Panamitsu (talk) 08:02, 27 July 2025 (UTC)[reply]

What color is the fading light? The white light section of the LED lamp article says they typically use phosphor, commonly yellow. This would glow briefly.  Card Zero  (talk) 08:12, 27 July 2025 (UTC)[reply]

When I look at the bulb there is a whitish-yellowish fade yes, but what I was referring to was the light in the whole room fading to darkness. A weird thing is that I cannot replicate the fade. If I turn the switch off and on there is no fade at all. But there is one sometimes, which makes me think that a) it only happens when the light has been on for a long time or b) it's some eye precondition. ―Panamitsu (talk) 11:03, 27 July 2025 (UTC)[reply]

If in doubt, ask your doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:59, 27 July 2025 (UTC)[reply]

If you look at a bright light source for a length of time, after discontinuing you will perceive an afterimage due to your photoreceptor cells getting "overexcited". This is a basis for some entertaining optical illusion effects: give the lilac chaser a try! --Slowking Man (talk) 19:39, 27 July 2025 (UTC)[reply]

Wow the lilac chaser is so cool! ―Panamitsu (talk) 22:33, 27 July 2025 (UTC)[reply]

Could it be leftover charge in smoothing capacitors powering the LEDs? cmɢʟee⎆τaʟκ 23:14, 27 July 2025 (UTC)[reply]

And in white LED lights there are fluorescent substances that continue to glow at fading levels for about a second as Card_Zero said above. Graeme Bartlett (talk) 23:27, 27 July 2025 (UTC)[reply]

It could be interesting to make a video of the situation and see if it matches what your eyes are seeing. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:14, 28 July 2025 (UTC)[reply]

Good idea although I had a try and my phone's autoexposure is too slow, giving a fade even when I don't see one. The phone records a fade also when I turn the lights on. ―Panamitsu (talk) 08:05, 28 July 2025 (UTC)[reply]

See if the camera app has a manual mode with exposure control. cmɢʟee⎆τaʟκ 10:55, 28 July 2025 (UTC)[reply]