I've got the similar symptom on a Sony 855GM laptop.
Low/None Backlight after resume.
ACPI backlight I/F doesn't work, Xrandr failed to work either.
(xrandr shows the backlight value is changed successfully but nothing happens)
After resume, I need to do a vbetool post in console mode and switch back to X to see the screen clearly.
I've got the similar symptom on a Sony 855GM laptop.
Low/None Backlight after resume.
ACPI backlight I/F doesn't work, Xrandr failed to work either.
(xrandr shows the backlight value is changed successfully but nothing happens)
After resume, I need to do a vbetool post in console mode and switch back to X to see the screen clearly.