PURE TWILIGHT Owner's Manual page 21

Active/Standby operation
Select Active operation to adjust the display settings that apply when
Twilight is switched on, or Standby operation to adjust the display
settings that apply when Twilight is in standby.
Brightness
By default, the display brightness is set to 'Automatic', which means
that the brightness adjusts to suit the light level around your radio. If
you want to change this setting, Tap Manual and use the +/- buttons
to adjust the brightness from 1 (low) to 10 (high). Push Select to
confirm, or tap OK. You can switch back to automatic brightness by
tapping Automatic.
Screen duration
GB
The length of time the display stays illuminated after a button is
pressed or context-sensitive button is tapped. Choose between
Always on (default) or Off after 7 seconds.
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