First, the excitation produced by different light sources may vary and not consist of “pure” LWUV or SWUV light, which generally have wavelengths of 365 nm and 254 nm, respectively. Differences in excitation wavelengths between lamps may produce inconsistent fluorescence reactions. Warm-up time, the materials used in the UV filters, and aging of lamps and filters can also affect the radiation output. Secondly, multiple defect centers may exist within the same diamond and produce different emission peaks simultaneously. To the human eye, multiple emissions combine to produce a single, albeit mixed, fluorescence color (e.g., blue + yellow = apparent whitish fluorescence). Visual evaluation of fluorescence does not allow for identification of multiple defects or irregular emission peaks. Finally, the distance between the radiation source and the diamond as well as the stone’s orientation (table-down versus face-up) may produce noticeably different fluorescence by changing the amount of excitation energy that interacts with the diamond.