Light · Chapter 11

Fluorescence, without the folklore

What ultraviolet light can reveal, when it affects appearance, and why the report line is not a verdict.

Fluorescence is a reaction to ultraviolet energy—not a quality grade and not the same thing as everyday sparkle.

What the report records

A report describes the strength of the reaction under long-wave ultraviolet light, commonly as None, Faint, Medium, Strong, or Very Strong. Blue is most common, though other colors can occur.

Lighting changes whether you see it

Daylight contains ultraviolet energy; many indoor environments contain much less. The same diamond can therefore react differently across sunlight, office light, jewelry-store spotlights, and ultraviolet lamps.

It is not automatically good or bad

Most fluorescent diamonds do not show an undesirable loss of transparency. Market preferences may still influence price, but the report word alone does not determine beauty or suitability.

Haziness requires observation

In rare cases, fluorescence may intensify pre-existing light-scattering effects. Check a Strong or Very Strong stone in neutral indoor light and daylight-equivalent conditions, comparing transparency and contrast rather than searching for a glow.

Let the actual stone answer

Compare the diamond beside a similar non-fluorescent stone when possible. If you like its appearance across useful lighting and it remains transparent, fluorescence need not be treated as a defect.

Worth remembering: Treat fluorescence as something to observe—not an automatic reason to accept or reject a diamond.

Essential language

Fluorescence: Visible light emitted while a material is exposed to ultraviolet energy.
Ultraviolet: Radiation beyond visible violet light that can activate fluorescence.
Phosphorescence: A glow that continues after the activating light source is removed.
Haziness: Light scattering that reduces crispness or transparency.

Questions to take with you

What strength and color does the report state?
Does the diamond remain transparent in daylight and neutral indoor light?
Can I compare it with a similar non-fluorescent stone?
Is a market discount influencing my view more than appearance is?