bright=$(brightnessctl get)
state=-1
thresh=(0 1 2 3 5 9 15 27 46 80 139 240 415 717 1240 2145 3710 6418 11100 19200)

for i in ${!thresh[@]}; do
    if [ $bright -ge ${thresh[$i]} ]
    then
        state=$i
    fi    
done

new=$(($1 + $state))
if [ $new -ge 0 ] && [ $new -le 20 ]
then
    echo $(brightnessctl set ${thresh[$new]})
fi