It writes with invisible ink made of special high-brightness ultraviolet viable compounds. This means the ink is completely invisible under normal light! Once the message has been written in invisible ink, it is time for the blacklight. So technically it is not really a "Black" light, but that's the popular term for ultraviolet energy. Near the visible spectrum of light. Flip the pen over, shine the light on the spot where the ink was used and your hidden message will be illuminated.
Dimensions: 5.31 in x 0.39 in x 0.39 in
Weight: 0.56 oz