Why models looks dark in a new created scene?

I created a new scene in my Unity project(Unity 5).
But models looks darkly in a new scene. I don’t know the reason. Can you explain about it?
All models were created, rigged, animated with Mixamo.

I know it’s very simple, but I’m a beginner without enough experience.

@tomas

You can fix this by setting lightmapping to automatic.
Window → Lighting and check Auto. If you find this useful please accept the answer.