Close lid and go away for a while. I have xfce4-power-manager set to switch off the display if the computer is inactive for 15min.
Come back and open the lid and the brightness is way way down and the controls don't work to change it.
[ 20260.867] (EE) intel(0): failed to open /sys/class/backlight/acpi_video0/brightness for backlight control: No such file or directory
[ 20260.871] (EE) intel(0): failed to open /sys/class/backlight/acpi_video0/actual_brightness for backlight control: No such file or director
The /sys/class/backlight/acpi_video0 directory doesn't exist.
However, there is a /sys/class/backlight/acpi_video1 directory.
Doing a echo 12 > /sys/class/backlight/acpi_video1/brightness causes the lcd to go back to bright.
So, something is removing the acpi_video0 dir/controls on monitor power off and readding them as 1 after turning back on.
Happy to provide more info or try things.
This seems to be fixed in 3.12.0-0.rc0.git25.1.fc21.x86_64 at least.