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If it is possible to set the brightness of your screen, it will dim when the computer is idle in order to save power. When you start using the computer again, the screen will brighten.

To stop the screen from dimming itself:

The screen will always dim, and dim more aggressively when choosing the “Power Saver” power mode. If you donʼt want the screen to dim at all, select the “Balanced” power mode instead.