Backlight on my laptop

I am new to Manjaro, not so new to Linux though barely above newbie level. I have Manjaro Plasma on a Lenovo Ideapad 330.

The backlight keys aren’t working, so I tried this: https://wiki.manjaro.org/index.php/Reactivating_the_Backlight

but after restarting it says it failed to load “?ightness”. I checked the grub file and the line is there.
Please advise.