Fn + F6 - backlight turns off immediately, image stays (visible if shine something at the display)
xset dpms force {off,suspend,standby} - backlight turns off slowly, image cleared.
How to programmatically just turn off backlight on Acer Extensa 5220 laptop in Linux? It should work fast and should not touch image (unlike xset method).
Ideally if I could rapidly switching backlight off and on emulate lower_than_minimum brightness level (ideally - to be hardly visible (but visible) at night).
intel_backlight from Intel GPU Tools can do this by 'poking' the register that controls the backlight directly, if you have integrated graphics. You will need to be root or make the program run as root, though. I'd recommend making it activate on an ACPI event, since those scripts run as root and can be configured to not be easily exploitable, should someone gain access to your account, rather than 'suid root'-ing it.
To turn off the backlight:
intel_backlight 0
To turn it back on: Just hit one of the brightness control keys, or use a script.
I've written a decent script to do this without the brightness level being increased or decreased on 're-enabling' in this other answer, where I also show how to set it up to trigger on an ACPI event.
The utility to control the backlight under X is called xbacklight. Unfortunately, it doesn't always work, depending on how well your video card is supported.
You may have more success with a driver-specific utility. For ATI cards, try radeontool. For NVidia cards, try nvidia-settings. There may be a similar utility for Intel cards.
If you have Acer laptop, use acer_ec.pl script to control laptop's Embedded Controller.
http://aceracpi.googlecode.com/svn/trunk/acer_ec/acer_ec.pl
acer_ec.pl := 84 00 will turn off backlight on my laptop
Warning Before using acer_ec on other laptop check that 84'th register is that you need. The script looks like one that can permanently damage the device if used without caution.
