Some people seek diamonds that produce this unique effect, while others definitely avoid it. The visible effects of fluorescence grades of faint, inert, negligible, and medium, can only be detected by a trained gemologist. A fluorescence grade of strong or very strong can make a diamond with a near-colorless grade look even whiter yet in some instances give the diamond a slight hazy or oily appearance. Diamonds with a strong or very strong fluorescence are priced slightly lower than other diamonds.

• For the purist, look for a colorless diamond with a grade of D-F and a fluorescence rating of faint, inert, none, or negligible.
• For an excellent value in a diamond with no noticeable color to the unaided eye, look for a near-colorless grade of G-I, and a fluorescence grade of medium or strong blue.
• Or, if you'd rather not compromise on color but would like to stay on budget, choose a diamond with a good cut, SI1–SI2 clarity, and consider going with a strong fluorescence. It will still be beautiful to the unaided eye and you may prefer the unique effect of a strong fluorescence.