Steps to reproduce:

1. Open attached project on a Mac
2. Open 'SOA' scene
3. Notice the scene is way too bright (first screenshot)
4. Go to Player Settings and change graphics API for Mac to any other
5. Notice the scene gets a little darker, though the lighting still seems off (second screenshot)
6. Play and stop the scene
7. Notice the lighting gets brighter again

Note: Doesn't look like the lighting itself depends on operating system. On Windows, the scene looks the same, the only difference is that changing graphics API for Windows doesn't seem to affect anything.

Reproduced with: 5.3.0f4, 5.3.0p1
Does not reproduce with: 5.2.4f1, 5.4.0a6