A Lid-Handler daemon that listens for dbus signals from UPower and sets the screen brightness to zero when the Lid is closed and restores it when opened.
go install github.com/d4ryus/lid-handler
Save (or link) lid-landler.service to ~/.config/systemd/user/ and make sure the lid-handler executable can be found, followed by:
systemctl --user daemon-reload
systemctl --user enable lid-handler
systemctl --user start lid-handler