The backlight has three features that you can adjust: the level of brightness (Brightness), how the standby backlight activates (Standby), and whether the backlight activates when you raise and turn your wrist (Raise to wake).
The backlight features can be adjusted from the settings under General » Backlight.
The Brightness setting determines the overall intensity of the backlight; Low, Medium or High.
The Standby setting controls the screen brightness when there is no active backlight turned on (e.g. triggered by button presses). The two Standby options are On and Off.
The Raise to wake feature activates standby backlight in regular time mode and activates backlight in exercise mode when your wrist is lifted to watch reading position. The three Raise to wake options are:
You can also set the backlight to be always on. Keep the middle button pressed to enter the Shortcuts menu, scroll to Backlight and toggle the switch to force backlight on.