Backlight Control Notes

System Setup

Get Correct Firmware

sudo apt-get install rpi-update 
sudo rpi-update

Permissions Change

sudo nano /etc/udev/rules.d/backlight-permissions.rules
SUBSYSTEM=="backlight",RUN+="/bin/chmod 666 /sys/class/backlight/rpi_backlight/brightness /sys/class/backlight/rpi_backlight/bl_power"

Disable auto poweroff

I also added a line to "/etc/lightdm/lightdm.conf" to turn off the automatic screen blanking, so the screen doesn't actually "blank" or "sleep" anymore, the button just manually turns the backlight on/off. Add the following under the "[SeatDefaults]" section in "/etc/lightdm/lightdm.conf".

[SeatDefaults]
xserver-command=X -s 0 -dpms

Backlight Control

echo 0 > /sys/class/backlight/rpi_backlight/bl_power
echo 1 > /sys/class/backlight/rpi_backlight/bl_power

Python Code

backlight = open('/sys/class/backlight/rpi_backlight/bl_power', 'w')
backlight.write('1') # turn on
backlight.write('0') # turn off
backlight.close()

Brightness Control

Must be between 1 and 255

echo 80 > /sys/class/backlight/rpi_backlight/brightness

Original Source