I tried to help a colleague to get their brightness hotkeys working on Ubuntu using the i3wm. I had googled and implemented a solution for it, but then forgot what I did. So, here it is, for the sake of Future Chris. This solution is applicable to the lenovo t470p and t480 at least.

place this script in /etc/acpi/brightness.sh:

#!/bin/bash

current_brightness=`cat /sys/class/backlight/intel_backlight/brightness`
max_brightness=`cat /sys/class/backlight/intel_backlight/max_brightness`

if [ $1 == "up" ] 
then
	new_brightness=$(($current_brightness + 100))
	[ $new_brightness -gt $max_brightness ] && new_brightness=$max_brightness
else
	new_brightness=$(($current_brightness - 100))
	[ $new_brightness -lt 0 ] && new_brightness=0
fi

echo $new_brightness > /sys/class/backlight/intel_backlight/brightness

and these under /etc/acpi/events:

/etc/acpi/events/brightness-down

event=video/brightnessdown BRTDN 00000087 00000000
action=/etc/acpi/brightness.sh down

/etc/acpi/events/brightness-up

event=video/brightnessup BRTUP 00000086 00000000
action=/etc/acpi/brightness.sh up

restart i3 and your brightness keys should work (I think)