light -P
No backlight controller was found, so we could not decide an automatic target. The current command will have no effect. Please use -L to find a target and then specify it with -s.
0.00
This happened with Mint too, I’m using gnome.
My build: xeon 2670 and Rx580
Update:
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 16384 x 16384
DisplayPort-0 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 598mm x 336mm
1920x1080 60.00 + 144.00* 120.00 119.88 119.98 99.93 50.00 59.94
1680x1050 59.88
1280x1024 75.02 60.02
1440x900 59.90
1280x800 60.00
1280x720 60.00 50.00 59.94
1024x768 119.93 99.99 75.03 70.07 60.00
832x624 74.55
800x600 119.93 99.86 72.19 75.00 60.32 56.25
720x576 50.00
720x480 60.00 59.94
640x480 119.80 99.83 75.00 72.81 66.67 60.00 59.94
720x400 70.08
DisplayPort-1 disconnected (normal left inverted right x axis y axis)
DisplayPort-2 disconnected (normal left inverted right x axis y axis)
HDMI-A-0 disconnected (normal left inverted right x axis y axis)
DVI-D-0 disconnected (normal left inverted right x axis y axis)