Write messages that only appear under UV light.
This marker is just like any other, except its ink is only visible under ultraviolet (UV) light. Anything drawn will be invisible to humans until exposed to UV light. The ink contains a photo-initiator which absorbs the high energy photons of UV radiation, but since the atoms in the ink want to be at their lowest energy state, the newly absorbed energy is forced out in the form of 2 new photons, one in the infrared range (i.e., heat) and one in the visible (typically blue/green range). The visible light emitted is called fluorescence. UV ink has found use in security purposes, as an authentication tool, protecting/hiding secret messages and even cleaning assessment.
You can use this marker to make hidden labels for your belongings, write secret messages, create UV art, and more.