Inspired by this post, I've made a new backlight utility that requires no setuid or udev rule: https://aur.archlinux.org/packages/blight/.

It's a convenience wrapper around the logind SetBrightness method. logind uses DBus policy to restrict the api to the owner of the active session – instead of users in the video group, for example.

It's less portable than the udev rule considering it depends on systemd, but I sort of expected a backlight utility to eventually appear using the new logind api. I haven't seen any, so I made this one. It's quite basic, but I suppose that's the point.

There are some minor reasons to prefer staying out of the video group. It becomes easier to allow access to the backlight without giving access to other devices in the video hardware group. Basically when your user belongs to the video group, find /dev -group video -perm -g w devices inadvertently become writable in addition to the backlight device – graphics devices, webcams, etc. It's not exactly a problem, but this is one way to avoid that. It also is one less step required to configure your backlight so that's nice too.

You can use it like blight set 25% or blight set 10% for a relative change. Use blight set -- -10% to pass negative percentages. Should work well on both X and Wayland. I replaced my old light keybinds with it in sway and it seems to be working well. Try it out if you want.