I'm using UBUNTU 10.04 LTS for desktop on my Acer 4738ZG Laptop which has a discrete video card of ATI 4750, with dedicated memory of 512Mb.
The first time I installed Ubuntu, (without the ATI proprietary driver for my video card) I could still adjust the brightness settings of my laptop for on-battery mode and on-AC mode. I will just adjust the horizontal bar to determine my desired brightness level.
After Installing and activating the ATI proprietary driver, I could no longer adjust the brightness level when I am in AC-mode. I could move the horizontal bar for brightness, but it doesn't do anything. In battery mode, everything is just fine. But I really want to trim down my brightness level on AC mode, since, I really find it uncomfortable to my eyes having the brightness level set to the max.
If you could provide help on how to adjust it without deactivating the Proprietary Driver for my ATI, it would be a big help for me.