The fluorescence of a diamond is the visible glow that occurs when it is exposed to ultraviolet (UV) light. Fluorescence is a naturally occurring phenomenon created from the mineral properties boron and nitrogen. It can appear in many minerals and gems.
Nearly all diamonds have some degree of fluorescence, although certain lighting conditions makes this difficult to see with the unaided eye. An ultraviolet lamp, however, can be used to reveal a soft-colored, fluorescent glow. Diamond fluorescence occurs in varying intensities and colors. Gemological laboratories rate the fluorescence of each diamond on a scale ranging from "None" to "Very Strong". Fluorescence is categorized as 'None' when there is no visible reaction under ultraviolet light. It will be categorized as 'Faint', 'Medium', 'Strong', or 'Very Strong' depending on how much glow is observed. The color range of the glow varies from standard blue to shades of green, white, pink, yellow, red or orange. See the chart below for more details.