PWM flicker on screens

In short: Many displays control brightness by switching the backlight on and off very quickly (PWM). At low brightness this flicker can cause headaches or eye strain for sensitive people.

In more detail: The flicker is usually too fast to be seen consciously, but eye and brain may register it anyway.

In Depth

• PWM (“pulse-width modulation”): Instead of lowering the current, the lighting is switched at high frequency. Darker means shorter on-phases.
• Frequency: High values (from about 1000 to 2000 Hz) are considered harmless, low ones (240 Hz and below, typical of many OLED phones at low brightness) problematic.
• DC dimming: Brightness is regulated through current, without flicker. Some monitors offer “flicker-free”.
• Test: Film the screen with a phone camera in slow-motion mode; stripes indicate PWM.
• Remedies: Higher brightness and reduce ambient light instead, devices with high PWM frequency or DC dimming, breaks, see preventing eye strain.
• Important: Sensitivity is very individual. See a doctor for persistent complaints.

See also: panel types