Today I would like to discuss with you an issue in relation to diamonds which is often misunderstood and over looked. This property can have a very large impact on the value of a diamond. This property is called fluorescence. Fluorescence is an optical property displayed by some diamonds whereby they may in certain light display a blue hue or glow when exposed to ultraviolet light. In the laboratory, special ultraviolet lamps are used to check for this but the sun is also a source of ultraviolet rays so diamonds will react in daylight also. Fluorescence is a diamond attribute listed on diamond certificates.The range of strengths as reported on laboratory grading reports is None, Faint, Medium, Strong, Very strong. According to the GIA approximately 25% of diamonds submitted to the laboratories for examination display some form of fluorescence. What impact does fluorescence have on the diamond appearance? What impact does fluorescence have on the pricing of a diamond? The presence of fluorescence in a diamond is generally considered to be undesirable . However in some circumstances where the diamond is of a bad quality fluorescence can in fact positively affect the overall look of the diamond. As a general rule the presence of fluorescence in a good quality diamond will lower its value.