I have a problem importing old Blender files that I created with Blender internal. I am now using Blender 2.8 and a Principled BSDF. When I render the object or set Viewport shading to Rendered, I don't see any shading. The objects don't react to the light. They look like materials in Blender Internal when the "shadless" option is checked. When I set the Viewport shading to Look Dev, the material looks much better, but even here it doesn't really react to the light properly. Newly created files are shaded correctly. What am I doing wrong?
I figured it out.
The main problem was that the unit system was set to "none". I set it to "metric" (Context Scene), and then scaled down my object to 0.1. Then the light worked as expected.
I also had to reduce the strength of the background to 0.2 (Context World).
Is there a good summary of what needs to be considered when switching from 2.79 to 2.8?