A different material for light vs shadows on an object - is this possible?

[paulinventome]

As subject suggests i am wondering if it is possible to blend between 2 or more materials based on the amount of light falling on an object? I am using VRay nuke but it's fairly comprehensive in terms of what it can access. However i've not found anything yet that can do this - any guidance or pointers would be super useful

thanks
Paul