how to get matte surface to get light?

[roysgi]

hi.
I am trying to make the floor surface in the right image (defined as a matte object) receive the light as in the left image, but without success. Any ideas?
Thanks

[hermit.crab]

Sorry to say, there's no such functionality as a "light catcher". I guess you could try rendering a LightSelect for the light separately (where the ex-matte object is identical via i.e. a Camera projection node) and comping after.