Weird terrain lighting

Good day,
I am using unity 5.4 and have some problems with terrain and lighting:

When I create a terrain and add a directional light to act as a sun, only everything in front of the camera is illuminated by the sun. Everything behind the camera is not illuminated. When I move the camera back, the illuminated area grows as you can see in the following video I made: - YouTube
What is the meaning of this? Can’t a directional light illuminate a 500 x 500 terrain? I am using an ambient lighting value of 1, because i would like to recreate the real life sun effect.

That looks like a reflection, not lighting… Mess around with your materials on the ground to see how they react, looks too reflective to me. Give the terrain some hills etc… and you should see that lighting is working ok.

Make sure that the textures on your terrain have a low metallic/smoothness value.