On my HP 62-a35er with integrated intel gpu and discrete radeon gpu fix is not 
correct. If I don't add kernel parameter acpi_backlight=vendor backlight is off.
As I tested at boot there are 4 items under /sys/class/backlight:
acpi_video0
acpi_video1
intel_backlight
radeon_bl1

After login brightness is controlled under acpi_video1 for some reason.
But brightness was set under intel_backlight to 4394 (maximum 4882).
Kernel version: 3.7.5-1 (currently I use Arch but believe that kernel in Ubuntu 
is roughly the same)

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https://bugs.launchpad.net/bugs/765438

Title:
  On startup, the backlight is off on laptop

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