ZDY Invisible Ink Pen 28pcs Spy Pen Invisible Disappearing Ink Pen with UV Light Magic Spy Marker for Secret Message and Kids

Is there a child in the world who doesn’t like the idea of sending secret messages in invisible ink? I haven’t met one yet. These pens will be a hit with any child who can write and who enjoys making up their own games. It’s the simplest thing but it really is fun. These would be a treat for kids who like secret spy games, crime-solving or super-hero games, for those who like passing secret notes or leaving clues that only certain people can see. Write notes with these pens and the words disappear almost immediately. But there is a special UV light at the other end of these pens. Anyone who has one of these can shine that light on the page where the invisible message was written and – voilà! – the message appears! I think these would make brilliant party favors or Valentines Day gifts. I’ll bet teachers could find lots of ways to use them in the classroom and they’d also make terrific end-of-the-school-year gifts to encourage kids to practice handwriting and spelling over the summer. About the wavelength of our lamp? We use lamps with a wavelength range of 420 nm-425 nm What is the principle of making the invisible ink appear? The ink we use is invisible ink. After you write, it will slowly disappear until you can't see the content of the writing. Then you need to press the pen to turn on the light to make the light glow, and use the light to observe what you write. The results of our experiment shows that the use of ultraviolet lamps with a wavelength of 420 nm-425 nm allows us to clearly see the disappearing ink, so the wavelength range of the lamp we use is 420 nm-425 nm