EDIT: thought u was using maya
rushed the post, so ignore everything i just said... lol
to adjust the levels where light hits the object, you can modify the color offset attribute of the shader.
this attribute on its own will brighten the entire model (or where the shader is assigned anyway) you can control the attribute to lighten and darken specific areas by mapping a ramp shader to it, since color offset is a single channel alpha the values of 0 and 1 will represent black and white- adjust the shader to how much you want to bleed light into it.
remember to only use Black and White (represents 0 and 1) this requires some playing around with but the result will be that you will lighten areas where its dark.