Determining paper fluorescence (F) is both art and science. Yes, there are guides - but for the average collector - not hard and fast standards that will give you a definitive answer to what you are looking at. Look on line for the "Gronbeck Jones Scale" (no relation) - it's very useful I find for grading. (I say look for it because I don't know where I found it).

I have a small sample file I use for testing made up of samples from Gronbeck-Jones and others. Use Unitrade for your guide stamps. Here's what I do........Hi-brite is the easiest. I use the centennial definitive 468B or 625 Xmas. For dull I go to 443 Xmas; F -> 561 Frontenac; light -> Fundy 726; LF -> 411i export; NF -> 505 Manitoba.

If you have difficulty in the middle ranges L-M you are not alone. It helps me to work with my UV light in total darkness but even then it's not totally guaranteed that you will get it right.

F is important because stamp values vary widely depending on it. I've just gone though a bunch of plate blocks, separating the $5 blocks from the $20 blocks - based only on F ratings.

davidgjones.authorsxpress.com/2012/05/14/david-g-jones-author-of-the-school-of-sun-tzu/