The brightness of your thermostat's screen is at maximum when you are using it. When the thermostat is in stand-by, by default, the brightness automatically adjusts to that of the surrounding environment. You can change the screen brightness using the Home + Control App: go to Settings, select "Manage my home", select the room in which the thermostat is installed, select the thermostat and select "Advanced", then you can turn OFF the screen brightness or set the desired level.
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