The backlight on the CM3-PANEL cannot be controled with normal DPMS. Instead,
the brightness is set using PWM on GPIO pin 22. The
`thermostat.backlight` program runs as a background process to manage
the PWM duty cycle. It exposes a D-Bus service to allow other programs
to control the backlight. It also watches for *xscreensaver* events to
detect when the screen is blanked and disable the backlight.
https://www.acmesystems.it/CM3-PANEL-7-BASIC_backlight
Dustin