I'm having issues getting Gnome's Night Light feature to work correctly with my monitor setup. I've recently switched to a new graphics card that has three DisplayPort outputs (in addition to one HDMI and one DVI). My monitors only support DVI and HDMI, so I bought three cheap DisplayPort to HDMI cables to connect them. Everything seems to be working correctly, except the Night Light filter in Gnome.
I initally thought I may be experiencing a known issue in Gnome 3.34.1 where Night Light stops working on Wayland, however switching to Xorg didn't help for me. Anyway, I believe that issue is now fixed. I'm using Gnome 3.34.3 on Ubuntu 19.10.
I switched back to the old graphics card (AMD HD 5870) and the issue went away, making me suspect either the new graphics card (AMD RX 570) or the cables. I haven't changed any drivers or firmware - I have the packages firmware-amd-graphics and xserver-xorg-video-ati installed. The output of
xrandr --verbose is at https://pastebin.com/E9cvPdZ0.
I tried various combinations of cables for my three monitors and this is what I found:
Connections | Result ------------------------+------- HDMI - - | Y - - DVI - - | Y - - DP-HDMI - - | Y - - DVI HDMI - | Y Y - DP-HDMI DVI HDMI | N N N DP-HDMI DP-HDMI DP-HDMI | N N N
In each case I restarted the computer to ensure the result could be consistently reproduced.
What technology does Night Light use to adjust the colour temperature of a display, and how could this be affected by the DisplayPort to HDMI cables I have? Should the feature be able to work with such a cable, and how can I find one that will work?