One of the more popular items we sell at Spectrum are pens that use invisible ink that only show up under ultraviolet light. The most popular ones actually have the ultraviolet light built right into the pen!
We recently added the new Ghost Writer as our latest Invisible Ink/UV light pen.
The Ghost Writer has all the features of older models but at a much lower price (under $4!). It has the invisible ink pen, the regular pen head, and the ultraviolet led flashlight. Batteries are included!
To use it, all you need to do is write whatever you want. You won’t be able to see it of course, its invisible! But then you shine the ultraviolet light onto the paper and voila!