Lighting in Look Dev is represented by an HDRI (high dynamic range image). The Look Dev view allows you to manipulate and easily switch between HDRIs to simulate different environments for the Asset you are working on.
This section provides information on how to create, import, browse and manipulate HDRI environments. See the following pages for details:
Is something described here not working as you expect it to? It might be a Known Issue. Please check with the Issue Tracker at issuetracker.unity3d.com.