Comment 8 for bug 876711

I have the same laptop (Dell Latitude D430) as Bobik-s and am experiencing what appears to be the same problem with a fresh install of , so I'll add some more information.

I tried adding the following kernel boot parameters one-by-one:
acpi_backlight=vendor,
acpi_backlight=video
dell_laptop.backlight=0
None of them make any difference. The gnome-settings-daemon PPA didn't appear to make a difference either.

The Fn+Up/Fn+Dn work correctly at the login screen, but only if the screen has not already automatically blanked. If the computer is left at the login screen for ~10 minutes, then it will automatically blank. Move the mouse and the backlight returns to partial brightness, but Fn+Up/Fn+Dn do nothing.

System Settings -> Screen contains a slider to adjust screen brightness. If I first click on it with the mouse, I can then use the Left and Right arrow keys to move the slider back and forth. After every 4 or 5 presses of the left (or right) arrow key, the brightness changes, alternating between brighter or dimmer. At either end of the slider the screen brightness appears to alternate between minimum and maximum. When the slider is 1 / 4 of the way across, the brightness alternates between 25% and 75%. When the slider is near the middle, the alternations are barely perceptible – perhaps between 40% and 60%

A question about something which may be related—the battery indicator at the top of the screen is always visible, even when plugged in. Isn't it supposed to disappear or change to indicate that it is running on AC? Clicking on the indicator shows “Battery (charged)”. Removing the power cord changes the text to “Battery (1:50 left)”.