Screen brightness changes automatically when I am using my browser. There is question about this matter but it is closed for being too specific . I think this is a general issue about Sony Vaio laptops with nVidia graphics. I had this problem when I used 10.04 and it still exists on 12.04. Since this is too annoying I just duplicate that question by picheto:
"I'm using Google Chrome version 21.0.1180.89 on Ubuntu 12.04 and my laptop is a Sony VAIO VPCCW15FL (spec sheet). My video driver is the propietary "NVIDIA accelerated graphics driver (post-release updates)(version-current updates)".
After installing Ubuntu, I discovered that neither the brightness control buttons (hardware) or the brightness slider (software) worked, and found out I could get the hardware buttons to work by installing the nvidiabl.deb package and oBacklight script. I'm using nvidiabl-dkms 0.77 and oBacklight 0.3.8. Still, the slider on the Ubuntu "Settings" does not work, but I don't care.
There is an annoying thing happening when loading certain pages in Google Chrome: the brightness goes up to 100% when loading the webpage or when leaving it (closing the tab or typing a different URL on the omnibox). However, the "brightness tooltip" (that default brightness notification) remembers the position it was set to, so if I adjust the brightness with the HW buttons, the level gets adjusted relative to the value it was set to before "going 100%".
I disabled the flash PPAPI plugin, but left the NPAPI plugin enabled, and the problem went away for pages with flash content. Still, the same thing happens when viewing HTML5 video, or when loading, for example, the Chrome Web Store or using the Scratchpad extension. I suppose it has to do with the rendering of certain elements using the GPU, but this is just a guess.
This brightness thing does not happen when using Firefox 15.0 or any other application I have used yet.
Does anybody know why this may be happening and what could I do to fix this without changing browser? Thanks a lot."