Visual evaluation of fluorescence is standard practice in gemological laboratories, and fluorescence color and intensity are often documented on laboratory reports. When selecting diamonds, jewelers also rely on fluorescence to ensure a good color match under a variety of lighting circumstances. The most common excitation source is a handheld UV lamp, which often has dual modes for long-wave (LW) and short-wave (SW) UV radiation. The typical color centers in diamond fluoresce more intensely under LWUV excitation. Fluorescence assessment relies mainly on visual observation at room temperature—fluorescence can vary in intensity and color at different temperatures—and sometimes requires a set of reference diamonds for comparison. Observation of fluorescence can be affected by three main factors: (1) the nature of the emission from the UV light source; (2) the nature of the defect(s) responsible for the fluorescence; and (3) methodology, including the viewing geometry and the distance from the radiation source. Within current industry practices, complications exist for each of these factors.