Enjoy... and please post any improvements or note any images! The reference vector is definitely off in this picture. The formula could be reworked to generate a reference vector from a pair of angles. Given that, one should then be able to get those angles to match two of the angles used on a light source making aligning with your light source much easier. (Alignment is important if you want to use a narrower spread of color like maybe in a gem picture; although if you just like the look but want more blue than red, rather than play with the reference vector, you could also change the colors around; i.e. swap blue for red.) Someday I may play around with that but if someone figures that out sooner, please post the amended formula. Bijouchat, I'd forgotten you do a lot of gems and jewelry; I'm eager to see what you do with it! Marc BTW I can't resist anymore... I used to have a cat name Bijou (for real; nice siamese)