When using my media keys, my backlight brightness is not changing until xfce4-power-manager sets the brightness to 45 in /sys/class/backlight/acpi_video0/brightness, at which point the screen will become dimmer and then the brightness won't change again until it hits 1 in /sys/class/backligh/acpi_video0/brightness. 

I seem to be able to set the brightness fine using xfpm-power-backlight-helper as root, but not if I try to use it through sudo from a regular user. 

If I'm not running xfce4-power-manager I am able to set the backlight brightness with my media keys, the brightness changes by 1 each time and the screen becomes noticeably dimmer for every 10 increments. I am also able to set my backlight brightness fine with xbacklight.