Sometimes, if you cannot find the options to reduce the system ( Intel Board ) brightness & Lock setting  in Ubuntu just following the steps,

phase 1 :

Open your terminal window, then open the grub file using gedit text editor,

$  sudo gedit /etc/default/grub

Find the line that says: 

GRUB_CMDLINE_LINUX="quiet splash"


Need to include the word acpi_backlight=vendor within the line,

GRUB_CMDLINE_LINUX="quiet splash acpi_backlight=vendor"


 Save and exit

:wq!

run the update-grub command
 
$  sudo update-grub
Generating grub configuration file ...

Warning: Setting GRUB_TIMEOUT to a non-zero value when GRUB_HIDDEN_TIMEOUT is set is no longer supported.

Found linux image: /boot/vmlinuz-3.19.0-15-generic

Found initrd image: /boot/initrd.img-3.19.0-15-generic

done


Finally, reboot your system
 
$  sudo init 6

If the phase 1 is could not be changed goes to phase 2 :


phase 2 :

Create a file 
 
$  sudo vim /usr/share/X11/xorg.conf.d/80-backlight.conf

Add below lines,


Identifier  "Intel Graphics"

    Driver      "intel"

    Option      "AccelMethod"     "sna"

    Option      "Backlight"       "intel_backlight" # use your backlight that works here

    BusID       "PCI:0:2:0"

EndSection

Save and exit.

:wq!

Reboot the system
 
$  sudo init 6

If the both phase 1 and 2 could not be changed just follow it.


phase 3:
 
$ sudo  echo 0 | sudo tee /sys/class/backlight/intel_backlight/brightness

Reboot the system
 
$ sudo init 6