Comment by jasim

Alongwith ddctrl (https://github.com/kfix/ddcctl), these aliases serve all my external monitor brightness needs:

    alias verydull="~/Software/ddcctl/ddcctl -d 1 -b 3 -c 15"
    alias dull="~/Software/ddcctl/ddcctl -d 1 -b 6 -c 35"
    alias decent="~/Software/ddcctl/ddcctl -d 1 -b 10 -c 40"
    alias medium="~/Software/ddcctl/ddcctl -d 1 -b 25 -c 50"
    alias bright="~/Software/ddcctl/ddcctl -d 1 -b 30 -c 50"
    alias morebright="~/Software/ddcctl/ddcctl -d 1 -b 35 -c 60"
    alias superbright="~/Software/ddcctl/ddcctl -d 1 -b 100 -c 80"