Cannot change the screen brightness. No such option in Settings/Power/ window.
No applet or widget in the top bar.
sys/class/backlight directory is empty
no backlight device detected
cannot install https://extensions.gnome.org/extension/231/brightness-control/
Running Debian Gnome 3.14.
Desktop PC with 4 GB RAM
Intel® Core™2 Quad CPU Q6600 @ 2.40GHz × 4
graphics: Gallium 0.4 on NVE7 (hardware: Nvidia GTX 650)
Debian GNU/Linux 8 (jessie) 32-bit
What have I done wrong? Thank you for any help!!