2D Unity - Light up object surfaces on collision

Hello, I'm trying to create an object that, on collision, will light up the surface of the object it collided with wherever the two objects met. For a visual example: ![alt text][1] [1]: /storage/temp/175556-shadersquestion.png I can't think of any implementation for this with the knowledge I have of Unity but I think the answer may be in the realm of 2D shaders. Does anyone have any idea of how to implement this or more resources on how to use 2D shaders with collisions? Thanks!