I was looking for the same and got after googling the same after a long time , hope this gonna help you out !!!
For Ubuntu #sudo apt-get install xbacklight
For CentOS / Redhat
#yum install xbacklight
then type this
xbacklight -set 50
there 50 stands for brightness range we can get it upto 100 from 0 .
you can also increase and decrease the brightness from present value to specified level.as you mentioned if you want to increase to 10% from current value of brightness then you can give this
xbacklight -inc 10
and to decrease 10% you can give this
xbacklight -dec 10