I have a terrain that is 20000 x 20000 and I use a directional light as sun. As it rotates it it shadows the terrain but still lights up the opposite side.
Look at image below:
Changing Shadow Distance to 20000 helps but then I get black artifacts on the terrain and changing the Lights Bias, Normal Bias and Shadow nera plane does not work no matter what I set those to…
Do anyone have any idea on how to shadow large terrains?
Anyone? Or am I the only one having this problem!?
I made the intensity of the light go to 0.0f and that fixes it… With Math.lerp, it should be a nice transition. Still if anyone has a better idea, feel free to share it 
I also lerp the intensity towards 0 at sundown and mix it with single color ambient light so it does not completely go pitch black dark. After the “sun” is down, I reuse the same directional light with a different color & less intensity as moonlight.
If you lerp the colors of the directional & ambient light as well, you can make nice transitions between night and day.