Screen Flicker Test

In short Most backlights do not dim by producing less light. They dim by switching on and off hundreds or thousands of times a second and varying how long they stay on, which is called PWM, and it is invisible to most people and a genuine headache trigger for some. If you get eye strain or headaches at low brightness but not at high, PWM is a real suspect, because the flicker gets deeper as brightness goes down. There are two ways to see it without any equipment. Wave a pencil quickly in front of the screen: a smooth blur means no flicker, and a row of separate pencil images means the backlight is strobing. Or point a phone camera at the screen and look for rolling bands. Both work better at low brightness. If you find PWM and it bothers you, the practical options are running the screen brighter and reducing ambient light instead, or looking for a display advertised as flicker-free or DC-dimmed — that specification exists precisely because this affects a minority of people quite badly.