Semen won't give off light like a glow-in-the-dark sticker, but it does fluoresce. In other words, it absorbs ultraviolet light and re-emits that energy.
Well as the title says why does it show up under a black light I was watching a crime show and they were using a black light to find semen in a rape victims.
If you've ever wanted to know how much semen there is in a room that looks clean, there's a simple trick to turn your smartphone into a black.
Does semen really glow in the dark? We've all seen the crime shows that have investigators wandering around a dark room with a UV, or “black light”, looking.
CSI - Semen glows in Black light. BLACKLIGHT TEST ON SIDEARMS BEDROOM! - Duration: 10:03. NobodyEpic 515,580 views · 10:03.