Sure. Here's a direct photo of an LED blinking at ~1Khz https://imgur.com/a/Kmx9Qhe https://imgur.com/a/Kmx9Qhe and here's one at 10Khz (you need to zoom in a b

Sure. Here's a direct photo of an LED blinking at ~1Khz https://imgur.com/a/Kmx9Qhe https://imgur.com/a/Kmx9Qhe and here's one at 10Khz (you need to zoom in a bit) https://imgur.com/a/Q7oqs9J https://imgur.com/a/Q7oqs9J When the light is passive (looking at the wall instead of the LED itself) the pattern is less obvious to the naked eye. Possibly invisible if there's enough ambient light. Around 20Khz the separation between bars is 1 pixel (on my camera) so you need to zoom all the way in to see it. BTW check you phone camera settings. Most phones intentionally correct for the bars around 50/60 Hz because that is the frequency of AC power so florescent lamps will cause the artifact. The effect is usually unwanted.