What is fluorescence in a diamond?
By Jared James · Last updated 21 May 2026
Definition
Diamond fluorescence is the visible glow a diamond emits under ultraviolet light, most often blue-white, though yellow and orange can occur. It is caused by structural elements within the diamond that absorb UV energy and re-emit it as visible light. Around 25 to 35 percent of gem-quality diamonds show some fluorescence, graded from Faint to Very Strong on grading reports. Strong blue fluorescence can make a slightly yellow diamond appear whiter in daylight, though in very strong cases it occasionally gives the stone a milky or hazy look.
Frequently asked questions
- Is fluorescence good or bad in a diamond?
- It depends on the stone. In colourless diamonds, strong fluorescence can occasionally cause haziness in bright sunlight, which lowers desirability. In diamonds with a faint yellow tint, medium blue fluorescence can actually make them appear whiter and is considered a benefit by some buyers. Faint fluorescence has negligible effect either way.
- Does fluorescence affect a diamond's price?
- Strong fluorescence in colourless diamonds typically carries a price discount because some buyers prefer to avoid it. For slightly lower colour grades, diamonds with medium blue fluorescence can attract a small premium because the fluorescence improves their appearance. Faint fluorescence has little effect on price.
- Can you see fluorescence in normal light?
- Not usually. Fluorescence is only visible under UV light sources such as blacklights, some club and gallery lighting, and direct sunlight which contains UV. In typical indoor lighting a fluorescent diamond looks the same as a non-fluorescent one.
Designing a ring
Talk through fluorescence with us
Tell us what you have in mind, even if it is only a budget and a piece of jewellery type, and we will help you weigh up the options. We reply to every enquiry, usually within one business day.
Contact the studio