Hey BiggestSmile,
I appreciate you deciding to refrain from bumping 
So looking into this issue, I found some information about Light Function Materials within the tooltip. I believe this to be your issue in conjunction with some post processing and light actors you might need to disable.
Firstly, in regards to the light function material, the tooltip reads, “Note that only non-lightmapped lights (UseDirectLightMap=False) can have a light function.” Since your light is set to Stationary, you are using lightmaps which means the light function will not work as you expect.
Your next issue seems to be with your Auto-Exposure setting within your Post Processing. In order to see your scene without this post processing effect, you will want to set the Min and Max brightness to a value of 1.0.
Let me know if you need help or have further questions.
Cheers,