BijanDiamonds.com Dictionary
Fluorescence:
Diamond fluorescence is a form of illumination that is created when a diamond is exposed to Ultraviolet (UV) light. Your diamond can be exposed to UL light from the "black lights" often found in nightclubs, the drying lights used in nail salons, fluorescent lights or direct sunlight. Diamonds emit light due to fluorescence when small amounts of the element boron are present in the stone when it crystallized deep in the earth where there is a lot of heat and pressure. Blue is the most common color of fluorescence, but other colors (yellow, greenish blue, green, white and pink) are also possible. In some instances it gives the diamond a slight hazy or oily appearance.

* Important Note *

* Diamonds with a strong fluorescence are priced slightly lower than other diamonds.

* Diamonds with a Very strong fluorescence are priced Extremely lower than other diamonds.

* Faint and medium are priced few percentage lower.

* Lower color stones like I-J-K-L color, Faint and Medium fluorescence are priced slightly higher.