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Ultraviolet light (UV) is used extensively for revealing luminescent effects. Two ranges of ultraviolet light are used in gem testing: long wave UV (LWUV) has a principal wavelength of 365 nm; short wave UV (SWUV) has a principal wavelength of 254 nm. The behaviour of gemstones in both LWUV and SWUV is observed and the effects can be useful as a pointer towards further suitable tests or as a back-up.

The invisible radiations emitted can be harmful to the skin. Do not place your hands under the lamp when switched on. Do not look directly at any ultraviolet (UV) light source as this can cause damage to the eyes. Most UV cabinets have a control filter to absorb UV energy and protect your eyes when fluorescence is being observed. If not goggles should be worn.


  1. Thoroughly clean the material under test to remove dust and organic materials
  2. Place on a black, non-reflecting pad, switch on either the LWUV or SWUV lamp work in subdued ambient light or use a light shield, to enable you to observe slight fluorescence or phosphorescence
  3. The fluorescent effects of both natural and synthetic materials can vary depending on their trace element content. Therefore any luminescent effect should only be taken as a guide and not as proof of identity.

Fluorescence in Diamond

Listed below are the abbreviations for describing strength of fluorescence that should be noted when a diamond a diamond report:
Non – No fluorescence
Faint – Slight fluorescence
Medium – Medium or Moderate fluorescence
Strong – Strong or Extreme fluorescence