Comment 3 for bug 1502662

step 1 : Open terminal and type the below commands.
step 2 : cd ..
step 3 : cd ..
step 4 : cd sys
step 5 : cd class
step 6 : cd backlight
step 7 : cd acpi_video0
step 8 : cat brightness

//Check the brightness level from the below commands and note it down.

step 9 : cat actual_brightness
step 10 : cat max_brightness

//Open editor and type the below script
step 11 : sudo echo <set the minimum value for brightness> > /sys/class/backlight/acpi_video0/brightness
//save the file as brigthtness.sh in home directory.
//type the below command

step 12 : crontab -e
//now the terminal will ask you to choose the editor in which you want to open the crontab. Choose nano.
//type the below script
# m h dom mon dow command to execute
  * * * * * ./brightness.sh || (cd && /home.cron)

step 13 : //type// sudo gedit /etc/default/grub
step 14 : change "quick splash" to " quick splash acpi_video0=vendor"
step 15 : sudo update-grub