xna - How do I autogenerate gradient lighting?

I am trying to think of a way to generate a gradient like this picture:

Something like this GetGradientTexture(360f,100(width),100(height)), or if i want a directional light (like a flashlight) 180f,10,200.

But I can't really think of a good way to do this. Does anyone have anything that can push me in the right direction?