Fluorescence is feature of the diamond "glowing" when illuminated by UV light. This feature is visible using special UV lamps. Fluorescent is about half of all diamonds, only 10% of diamonds are visible due to strong fluorescence in daylight.
Fluorescence is predominantly blue, but it can also be green, yellow, orange or milky white.
Fluorescence also has a relatively large influence on the price of diamonds, while in the case of top-quality investment diamonds (D, E, F), this feature is undesirable and affects negatively their price, for finely toned colors (I, J, K, L ...) on the contrary, the diamond can be more appreciated because it makes it more colorless.
Diamonds with fluorescence are especially attractive for jewelry, where they do the same service as diamonds without fluorescence, but at a noticeably lower price.
Generally, the top color diamonds without florescence (ie. "Non" or "nil") are sold at 10 to 20% higher prices than diamonds with fluorescence.
Conversely, in the finely-toned colors, the very strong blue fluorescence is estimated to be about 5% higher than that of diamonds without fluorescence.