DO NOT USE THAT LIGHT TEST!!!! There are very few boards that light will shine through. Like stated above any board that is brown on one side will be low grade. The link that Ryanw posted is the best way to start to learn. Grading boards is the hardest part of scrapping electronics. If at all possibale try to find a local buyer by you, that way they can work with you on gradding the boards the way they want them. Every buyer seems to have a diffrant grading system. Also when Ryanw talked about boards being green they are green all the way through, very few that are green on both sides and brown in the middle will be mid grade but thiere are all ways exeptions. One more thing, just because there is gold on the board dose not make it a mid to high grade board.