Fluorescence in a diamond refers to the visible glow that occurs when the diamond is exposed to ultraviolet (UV) light. This glow is created by the natural presence of minerals such as boron and nitrogen within the diamond. Fluorescence can be found in many minerals and gems.
Nearly all diamonds have some degree of fluorescence, although it may not be visible to the naked eye under certain lighting conditions. An ultraviolet lamp can be used to reveal a soft-colored, fluorescent glow in the diamond.

Diamond fluorescence occurs in different intensities and colors. Gemological laboratories assess the fluorescence of each diamond on a scale that ranges from “None” to “Very Strong.” When there is no visible reaction under UV light, the diamond’s fluorescence is categorized as “None.” If there is a visible glow, it will be classified as “Faint,” “Medium,” “Strong,” or “Very Strong” based on the intensity of the glow. The color of the fluorescence can range from blue to shades of green, white, pink, yellow, red, or orange.