Hello,
I wanted to control screen brightness with keyboard, but no shortcut key (by default) and xbacklight does not work on my DevTerm-A06.
So I found another project that works; light(https://github.com/haikarainen/light).
‘light -A %n’ to increase screen brightness, and ‘light -U %n’ to decrease
(%n needs to be more than equal 12 on DT-A06)
I set xfce4 keyboard shortcut,
Shift + Vol_Up(Fn+Vol) to more brighter,
Shift + Vol_Down(Vol) to less brighter.
That works perfect for me 
If There are another solution, please let me know.
(Sorry for poor English)
Thank you.