xrandr brightness settings permanent

[Riccardo Berto]

I have a low quality screen. It's very bright, even at minimum settings 
in the monitor menu. I'm able to reduce the brightness with `xrandr 
--output HDMI-0 --brightness 0.25` but sometimes the brightness goes 
back to the default levels when downloading something from the browser 
or doing peculiar interactions with the Xorg server, like opening the 
file manager. I guess this is caused by a re-read of the xorg.conf file 
under certain circumstances that I'm not aware of.
The question is: is it possible to make the previously mentioned xrandr 
command permanent via some /etc/X11/xorg.conf.d/ conf file?