I have a Dell XPS 13 Laptop (old series) with ArchLinux and Gnome 3.18. I've read in official gnome 3.18 release notes that
If a light sensor is present, GNOME will now automatically adjust the display brightness in order to adjust for the ambient light level.
Can be tested using a ColorHugALS device for those who don't have built in hardware.
Windows 8 compatible hardware is supported.
A switch in the control center's power panel allows automatic display brightness to be turned on/off.
My ambient light sensor is not supported by Linux kernel out of the box, however I have compiled and installed / loaded this module and now my sensor appears as
/sys/bus/acpi/devices/ACPI0008:00/. For example I can do
$ cat /sys/bus/acpi/devices/ACPI0008:00/iio\:device0/in_illuminance_raw 153
and read current raw illuminance.
However this seems not to be detected / supported by gnome as I still don't get a "switch in the control center's power panel" and display brightness is not automatically adjusted.
How can I make it work?