Can't control the display brightness on Lenovo X1 yoga OLED

I just stumbled on this question, looking for an answer I gave a while ago regarding OLED screens in X11. See here. I normally bind some variations of the command to some keys, so I can switch fast:

xrandr --output eDP1 --brightness 1   # no dimming
xrandr --output eDP1 --brightness .5  # dim to half 

Entering xrandr by itself shows the device-name to be used (eDP1 or eDP-1 or the like). The number can be anything between 0 and 1.

Floating point numbers can be used. If the value is greater than 1 screen goes above normal brightness but colors become saturated.