Why does my iMac 2015 light up the display when idle?

Question

iMac

Why is the display backlit on iMac 2015 in standby mode?

Moreover, when sending it to sleep, it normally goes out, after a while a light appears on a dark screen. Approximately similar as here in the screenshot, only without the white stripe. Especially annoying at night))

Any ideas?

Answer 1

I had a similar phenomenon in 2017, it just looked like this: you send it to sleep - okay, it went out, after a few minutes the entire screen may start to glow with a clear color. Googled, saw that the problem exists, but no one knows what it is connected with.
The problem ceased to be observed after the processor was replaced, the HDD was pulled out, and a Samsung SSD was installed instead of the standard SSD.