Diamonds that are said to be fluorescent contain particles that emit a visible (usually blue) glow when exposed to UV lighting. None is considered the best, followed by Faint, Medium, Strong and Very Strong, we recommend None to Medium.
In rare cases, high levels of fluorescence can make stones appear milky or hazy, although for the most part fluorescence does not generally impact beauty or sparkle and can even make some lower colours (I, J, K, L, etc.) appear more colourless or white. Nonetheless, fluorescent diamonds are usually cheaper and provided the effect is not readily visible may offer good value for money.