This one is from way back: http://www.renderosity.com/messages.ez?Form.ShowMessage=1445452 The True Ambient 'light' reflecting off of mirrors is always diffuse as far as I can tell. There are no perfect reflections of rays and beams. However, the diffuse light can be focussed to some degree, both by refraction and curved mirrors. You might call it semi-caustic, unlike some of the posts here which are very caustic. ;-)