Comment 32 for bug 850065

toshiba_acpi probably isn't going to help. Most newer models I've looked at don't support modifying the brightness level via the interface it uses, only reading it, and yours doesn't appear to be an exception.

Please try the following. First, run these commands:

  cat /sys/class/backlight/acpi_video0/max_brightness
  cat /sys/class/backlight/acpi_video0/brightness
  cat /sys/class/backlight/acpi_video0/actual_brightness
  cat /sys/class/backlight/acpi_video0/bl_power

Please provide the output you get from these commands. Then try running

  echo n | tee /sys/class/backlight/acpi_video0/brightness

replacing "n" with various values less than or equal to the number you got from the max_brightness file (you might avoid using 0 in case it turns off the backlight). Does the backlight level change? If not, please attach the output of dmesg after writing the values to the brightness file.