$ xfce4-power-manager --debug > xfce4-power-manager-debuglog

(xfce4-power-manager:4845): xfce4-power-manager-WARNING **: could not map keysym 1008ffa8 to keycode


** (xfce4-power-manager:4845): WARNING **: could not get output property
xfce4-power-manager-Message: Set kernel brightness switch to 0

(xfce4-power-manager:4845): xfce4-power-manager-WARNING **: Failed to get keyboard max brightness level : Method "GetMaxBrightness" with signature "" on interface "org.freedesktop.UPower.KbdBacklight" doesn't exist

^Cxfce4-power-manager-Message: Restored brightness switch value to: 1