Fluorescence is a diamond's reaction to ultraviolet (UV) light, causing the stone to glow in various colors. If you place a diamond under UV light and it glows a bluish color, it may cause the diamond to look dull under sunlight.
Any diamond within the Color range of D, E, F, G, and H that has a fluorescence grade of medium blue to strong blue, according to industry standards, should have a market value 8% to 15% less then a diamond without fluorescence. DoW strongly suggests staying away from these diamonds, since they will appear very dull and have little to no sparkle.
Since fluorescence is NOT desirable, for diamonds within the Color range of D, E, F, G, and H. DoW recommends that you look for diamonds with No (None) Fluorescence to Faint Fluorescence. A diamond with no florescence would be an ideal buy. But, there is an exception. If your diamond's Color grade is within the range of I, J, or K, fluorescence will make the diamond appear whiter, and it is OK to purchase this diamond.