Can I turn it off/on from Raspbian?
No, not yet! But soon.
Can I control the backlight?
An update to turn the backlight on/off is in the pipeline ( currently
available in cutting-edge firmware ) but brightness control is not
supported.Can I turn it off/on from Raspbian?
Why hasn’t this been updated? You can both turn backlight on/off completely and control brightness gradually by changing files in /sys/class/backlight/rpi_backlight/
I know it has been said that changing backlight brightness wouldn’t even be possible but changing the value in /sys/class/backlight/rpi_backlight/brightness from 255 to 100 certainly changed brightness for me.
Setting /sys/class/backlight/rpi_backlight/bl_power to 1 turns the backlight off, setting it to 0 turns it on.