The normal diffuse and ambient settings for an object=100. If they add up to greater than 100 the object appears to give off more light than it takes in. Diffuse is the part of the object the sun hits. Ambient is the shadow side of an object. Things that are glowing don't have a shadow side. If your diffuse and ambient settings are equal your object won't have a shadow side.
For irregular objects do like pogmahone said. It is also good to check the material settings of you original object and turn off cast shadows, receive shadows, self shadows.

Message edited on: 11/06/2004 17:49