The real problem with the Linux kernel. Default kernel version could not identify the Intel driver. You can find that /sys/class/backlight will be empty. Brightness control folder and files should be reside here.
How to solve it?
Solution is that upgrade the kernel of Debian.
Update the kernel
Check the current version of kernel using following command in a terminal,
It will show the kernel version information.
Update sources list
Open following file using any editor, here I used leafpad editor,
Add following lines,
deb http://http.debian.net/debian jessie-backports main
deb-src http://http.debian.net/debian jessie-backports main
Save the file and close it.
Install the kernel
Check the kernel versions available,
apt-cache search linux-image
It result list of kernel versions.
Install the latest version of kernel,
apt-get install -t jessie-backports linux-image-amd64
Restart the system
Check the new kernel version
Visit again the folder /sys/class/backlight and you can find a new folder intel_backlight. It means the new kernel identify the Intel driver.
Change the brightness
and add the value 400. Save and close the file.
Now screen brightness under your control.
You can manage screen brightness using xrandr and xbacklight commands from terminal.
How to upgrade the Linux Kernel of debian 8 jessie