Many people believe that the color of fluorescent diamonds in the past have been over graded. e.g. that a G color strong blue fluorescent diamond may be a H in light with no UV (e.g. most LED lighting). This tray can be placed between a light source and the diamond to screen out shorter wave lengths than 400nm that cause a lot of blue fluorescence. Using a non-fluorescent color comparison diamond you can insert, remove, insert the tray and check to see if the fluorescent diamond suffers a drop in color.
Note: new research has shown that visible and near visible violet light causes beneficial color enhancement in out-door and many in-door environments improving the apparent color above grades given by labs. All labs now use low UV emitting grading lamps.