You can select the object, open the Render Tree, disconnect what you had connected in the Photon input of the material node.
Then create a Photon Irrandiance node, connect it into the Photon input of the material node. Now you can control separately the photon contribution contribution of the object.
If you don't want to do that, you can still try messing the Radiance setting of the surface shader you're using (Phong, Blinn, Constant...).
Cheer
Bernard