Home What is PWM flicker?
What is PWM flicker?
Many screens do not dim by making the backlight weaker. They dim by switching it on and off very fast and changing how long it stays off. This is pulse width modulation, or PWM.
How it works
The backlight runs in cycles, often hundreds or thousands of times a second. In each cycle it is on for part of the time and off for the rest. The share of time it is on is the duty cycle. At full brightness the light is on for all or most of each cycle. Turn brightness down and each off period gets longer, so the screen looks dimmer on average.
The switching is too fast to see as blinking. Some people report eye strain or headaches at low brightness settings.
Why low brightness matters
At low settings the off periods are longest, so any flicker is deepest there. That is why you will see advice to keep a screen's own brightness higher and dim another way.
Other ways to dim
- Software dimming. An app darkens the picture itself, with a gamma change or an overlay, while the backlight stays at a higher setting.
- Hardware brightness over DDC. An app sends the monitor a brightness command, the same as pressing its buttons. It changes the backlight setting, so the monitor dims the way it always does.
- DC dimming. Some monitors lower the current to the backlight instead of switching it. Few makers say this in plain words; in this directory only AOC names a DC backlight.
Which apps say they act on it
4 of 15 apps say so in their own words: BetterDisplay, CareUEyes, CircadianShield, Iris. See their exact quotes on the PWM flicker page, and monitor wording on the home page.
This page explains a mechanism. It is not medical advice, and nothing here says any product fixes anything.