What is a blacklight and how do you make one? This is the topic of a recent MacGyver episode in which he quickly creates an improvised blacklight to find hidden messages on a wall. You can watch the scene here-and a disclaimer, I am currently the Technical Consultant for the show. But still, there's lots a great science in this one little scene. What is "Blacklight"? OK, it's not really a black light. It's better to call it what it is: ultraviolet light. Let's start with a quick overview of light.