Blending and Decaying Alphas

Hello,

I am fairly new to Unity so forgive me if this is a newbish question.

Basically I am trying to create a program where different objects emit "light" that decays exponentially away from the center of the object, but that also have a strict cutoff radius. I would also like lights of different colors to blend at intersection. The objects position and the initial brightness can be changed via the user interface if that matters. It is also important that the brightness decay exponentially rather then inverse square or linearly.

How should I go about trying to accomplish this, and what sections in the manual would help me out?

I tried using light source components but I couldn't get them to blend correctly or at all, so now I'm thinking that I should use particle emitters, but honestly I don't know where to start.

Any ideas or any help at all would greatly be appreciated.