Comment 1 for bug 1083036

Have the same issue but found a way to do it. Created 2 shell scripts and put them in /usr/bin and then use the reflex "start application (advanced)" to run them when pluged or unpluged

This is where I got the idea from (askubuntu.com):

...one more way we have to do this is with another new program named as xbacklight , open your terminal and type this

sudo apt-get 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