Lots of controversy surrounding diamond fluorescence. Lots of diamond markets discount the price or value of diamond fluorescence. However, fluorescence has a added benefit to identifying and purchasing diamonds. Approximately 35% of all natural diamond exhibit fluoresce.
According to the GIA here are the fluorescence scale: None, Faint, Medium, Strong, Very Strong.
I personally love fluorescent stones. The reason being it helped me pass my Diamond Diploma program when I was separating natural, CZ, and Moissanite stones. Once a diamond exhibited fluorescent I knew it was real.