And from the NEWS file for systemd 243:
* systemd-logind now exposes a per-session SetBrightness() bus call,
which may be used to securely change the brightness of a kernel
brightness device, if it belongs to the session's seat. By using this
call unprivileged clients can make changes to "backlight" and "leds"
devices securely with strict requirements on session membership.
Desktop environments may use this to generically make brightness
changes to such devices without shipping private SUID binaries or
udev rules for that purpose.
It's clear that it's not just displays.
>
> Oh and yeah, IMHO another argument could be that obviously at some
> point
> the LED management could be removed from those user space tools, as
> the
> kernel would already know about them.
>
> After all the LED class devices should be there for a reason ;-)
>
> Cheers,
>
> Manuel
>
