Dell Inspiron 15 (Inspiron 3521). The graphic card is the integrated Intel graphic card: Intel® HD Graphics Screen is: LED Backlit Display with Truelife and HD resolution Install Ubuntu 12.04 downloaded in Sep. 2013. If I use the function key Fn+F4/F5, it shows the brightness bar. But there is not effect. The brightness stays the same.
I googled. One suggested solution to use grub: acpi_osi=Linux or acpi_backlight=vendor, You know there are many variants. Then I restarted my laptop: after the menu, it is stuck there. Then I can only force to turn off the laptop, and restart to choose the recover mode. Ubuntu will start. Brightness still cannot change. I change the grub setting back. Now the laptop can start correctly. Of course, brightness adjustment does not work.
The second suggested solution is to install xbacklight. It cannot work.
I used xrandr -q | grep " connected" xrandr --output LVDS1 --brightness 0.8 it seems to work. But I think it adjusts not brightness, but contrast. So actually it looks not good.
Then what should I do? Now I do not want to use the newly bought Dell laptop any more. Or I switch to Window? Oh, I like Ubuntu!