The invisible ink in this pen contains special brightness ultraviolet viewable compounds. Completely invisible in normal light, the secret messages can only be revealed by the beam of the UV blacklight. This beam consists of ultraviolet energy close to the visible spectrum of light which causes particles within the ink to fluoresce, illuminating the message. It's always time to have a laugh with NPW whether it be a birthday, office prank, sleepover, party or just because you want a mega LOL. NPW lives and breathes cheekiness. Entertain friends with hilarious gifts and gadgets that will crack them up! There is never a dull moment with NPW in your life!