Steps to reproduce:
1. Create a new Unity project using the Lightweight template for VR
2. Run the Scene in Windows Standalone (OpenVR)
3. Observe / capture scene
4. Switch platform to Universal Windows Platform
5. Run the Scene for Windows Mixed Reality
6. Observe and compare the scene

Expected results: Scenes should be pretty much be rendered identically, same as in the scene view
Actual results: Windows Mixed Reality is significantly darker than either the scene view or OpenVR

Note: Lightweight RP Template for VR introduced in 2018.1

Reproduced with: 2018.1.9f1, 2018.2.1f1