Since I bought my new laptop a few months ago and installed Ubuntu 12.04 on it I have not been able to adjust the brightness of the backlight. Until yesterday, this had not bothered me much; I typically use my laptop in well-lit rooms so the extra brightness was a minor annoyance. Yesterday at the SciPy conference it became an issue while sitting for extended periods of time in the darkened main ballroom. A bit of searching led me to this question on AskUbuntu, which is not specifically about my laptop model but provides a general fix that worked for me. The fix, summarized here:

  1. Edit /etc/default/grub
  2. Change the line GRUB_CMDLINE_LINUX="" into GRUB_CMDLINE_LINUX="acpi_osi=Linux"
  3. Run sudo update-grub
  4. Restart the machine

This is a known bug in Ubuntu with no definite timeframe for a fix.