How Does Sunlight Affect Diamond Fluorescence?

Diamond color is not related to fluorescence; it is a separate element referring to the diamond’s ability to fluoresce under ultraviolet (UV) light. Although the sun emits some UV rays in sunlight, it is generally not enough to detect most fluorescence. However, when exposed directly to UV light, many diamonds will glow with a blue coloration. Blue is the most commonly displayed diamond fluorescence, but other hues are possible. Diamond fluorescence grades include None, Faint, Medium, Strong, or Very Strong.

Fluorescence’s Impact

Although fluorescence is a characteristic that can be measured, it is rarely an issue when selecting a diamond. This is because diamond fluorescence is rarely detectable to the eye. The impact of fluorescence on the value of a diamond depends on its noticeability. Since diamonds graded none or faint fluorescence have little effect on color, the value of these diamonds is not affected. However, some higher grade stones such as those rated D to G may contain a milky white appearance under UV light. This can greatly reduce the stone’s value. On the other hand, fluorescence often adds value to stones with a hint of color, such as I-color and below, as diamond fluorescence often gives the diamond a brighter appearance.

Diamond Fluorescence In Direct Sunlight

Although the sun’s UV rays don’t affect most diamonds, diamonds with very strong fluorescence glow blue under direct sunlight. While the amount of fire and brilliance is not changed, the diamond’s color appears blue. However, even very strong diamond fluorescence will still be faint in most sunlight. Ambient sunlight, such as the light that passes through windows into buildings, will not alter the diamond color. Therefore, while a diamond’s fluorescence may lower the value of a stone, it will still appear gorgeous with great sparkle in nearly every situation. For this reason, many shoppers on a budget will opt for a diamond with strong fluorescence when designing a custom engagement ring.

Learn more about diamond fluorescence in the Adiamor Diamond Color Education guide.