I have been install Kubuntu 17.04 on my laptop and I want to set a specific screen brightness percentage for every power saving profile as below:

1 - On AC Power: 25%
2 - On Battery: 20%
3 - On Low Battery: 5%

https://docs.kde.org/trunk5/en/kde-workspace/kcontrol/powerdevil/energy.png

The problem is the brightness bar doesn't show any percentage as shown below:

https://i.stack.imgur.com/ksPSw.png

I don't know why it doesn't appear like this one?

http://blog.broulik.de/wp-content/uploads/2015/02/pmdisabled4.png

Please advise!

Thanks.