How can I use Python and PIL to draw a shape that would simulate how light/shadow is cast around shapes/objects from a point in a (2D) image?

Question

What I have is a black and white image of shapes, e.g. shapes.

And I would like to be able to, for any given point within the (white/valid portion) image, put a circle representing a radius of light cast from a point, e.g. points A & B and radii A & B.

From there, I would like to generate a shape/mask, that correctly displays where the light would be and where shadows would be cast, e.g. cast.

Finally, I would like to create a final mask of this shape, e.g. final.

The initial shape layouts, the points, and the 'light' radii for each point would all be variable.