XFCE4 Power Manager Brightness Panel Plugin

[Lars Noodén <lars.nooden@gmail.com>]

I've got xfce4-power-manager 1.4.1-1 in xfce4 on jessie and would like 
to find a way to dim the LCD backlight.  I'm not seeing a brightness 
panel anywhere like this one:

	http://docs.xfce.org/xfce/xfce4-power-manager/brightness

nor does the backlight respond to the usual shortcut keys for dimming.

What needs to be added or configured to get a brightness slider or other 
brightness control for the backlight?

Regards,
/Lars