What Is Fluorescence Grading Scale

Jewelers can measure the level of fluorescence under ultraviolet light. The example of ultraviolet lights can be seen in the clubs where people’s clothes, teeth glow in a special white bluish light. This is the ultraviolet light.

It is the same with diamonds. As soon you turn off the ultraviolet light they stop emit fluorescence.
So blue diamond fluorescence can only be seen under UV light.

Some of the diamond labs still do not agree whether the fluorescence affect the diamond clarity or not. GIA has published some studies about  diamond fluorescence and diamond clarity. They claim that only 1 % of polished diamonds have the amount of fluorescence that can affect diamond clarity.
GIA claims that especially diamond grades I through K have the most of the effect from fluorescence is a positive way. The color of those rings looks clearer when the fluorescence was in high levels. But usually the fluorescence does not affect the diamond clarity.

Each diamond inspected under strong UV light emit none through very bluish light. It depends on quantity of boron atoms each diamond has.
GIA and other diamond laboratories describe how much fluorescence a diamond has. Different fluorescence grades in the GIA diamond certificates are
None
Faint
Medium
Strong
and
Very Strong
Especially some jewelers still think that fluorescence is a bad and negative factor of each diamond. This might not be true.
There are still different amount of UV light used in different diamond laboratories during the diamond grading. So the grading is also different from laboratory to laboratory.

Diamonds with lower grade color might get a higher color or clarity grade because of the fluorescence effect and this might be the reason that the true diamond values is not correctly established.