A certified diamond is rated on many different parameters, including diamond fluorescence. Diamond fluorescence is the way that the diamond changes colors depending upon the light that they come in contact with. Diamonds have a natural blue fluorescence under ultraviolet light, but the level of diamond fluorescence can actually vary from diamond to diamond and can affect the value and the enjoyment of your diamond.
One thing that you need to consider when you purchase a diamond is the level of diamond fluorescence. It can completely change the look of your diamond from place to place, which can significantly affect your satisfaction with the diamond. Some types of diamond fluorescence actually increase the value of your diamond. For example, a blue fluorescent diamond is actually worth more than a yellow fluorescent diamond. The diamond grading report will grade the fluorescence and you can ask the jeweler to show you how the diamond looks under different lights as well to make sure that you get a diamond that you enjoy the look of.
A diamond fluorescence of J to M only has a moderate amount of fluorescence and this is not an amount that affects the diamond in a great way. A diamond fluorescence of D to F, however, can significantly impact the look of the diamond making it look milky or cloudy, because it impacts the flow of light through the diamond. Either way, you want to look at the diamond that you are considering purchasing under several light sources to make sure that you like the look of it.