Flourescence

Fluorescence describes the illumination created when a diamond is exposed to ultraviolet light. Faint of medium fluorescence rarely affects a diamond's appearance, but stronger fluorescence may have an impact on the perceived color. For instance, with a yellowish diamond with a strong blue fluorescence, the fluorescence can be strong enough to mask the yellowish tint when viewed under fluorescent lighting. When looked at under different lighting, that same diamond can look very different. Also, the opposite is possible as well - diamonds that fluoresce yellow may look more yellow under ultraviolet lighting, and whiter under incandescent lighting.