Steps to reproduce:

1. Open attached project using Unity 4
2. Open scene "inter", select "Spotlight" and notice that it's intensity is 3.4
3. Bake lightmap
4. Take a screenshot of ligtmap for later comparison
5. Open same project with Unity 5
6. In hierarchy, select "Spotlight" and notice that it's intensity is 6.8 (this is expected after upgrade from 4 to 5)
7. Bake lightmap and notice that it's much brighter than in Unity 4
8. Set light intensity to 3.4 (like in Unity 4) and bake light map again
9. Notice that lightmap is much closer to Unity 4

Reproduced with: 5.3.5p6, 5.4.0f2, 5.5.0a4