The keyboard backlight of my macbook air is always 100%, and the xfce power manager does not provide a way to control that. The keyboard backlight keys on the keyboard do not do anything. Also, when the display is turned off automatically after some inactivity time, the keyboard backlight stays on. This should not be - it should be turned off and on like the display backlight.
This should be improved or even fixed now in git master. Could you give it some testing?
sorry, I'm using Mate now instead of XFCE.
Since it's in xfpm now and you're happy with Mate, marking resolved. ... I should check out Mate sometime.