Brightness changes in Ubuntu but not on Windows

Brightness changes in Ubuntu but not on Windows

I have Ubuntu 12.04 installed on my VAIO S series (VPCS149FJ) that came
originally with Windows 7 SP1. I installed it with Wubi.
I can't change brightness in Windows with the Fn+F5, F6 hotkeys and even
from the control panel. I recently did a Windows reinstall but I believe I
have the proper keyboard driver (Fn+F3, F4 works for volume control) and
proper monitor driver (Generic PnP monitor matches the Monitor layer in
the fully expanded Device Manager screenshot provided by VAIO).
However, in Ubuntu I can change brightness in the preferences, and the
unchangeable brightness in Windows is much darker than the default
brightness in Ubuntu (set to the brightest).
I've looked for information about this issue in Ask Ubuntu but all I can
find is that brightness doesn't change in Ubuntu, not in Windows.