IIRC it was the opening scenes of Basic Instinct (?) where they used the hand-held UV flashlight to show that the dead guy produced and spread a decent amount of seminal fluid all over the bed. The splashes all glow bright white.
Since then, this meme has been used in a lot of Hollywood shows.
I assume this is the concept the OP is asking about.
What component of semen, apparently not found in blood, fluoresces?
Whenever this topic comes up, I always feel the need to point out that laundry detergent also fluoresces under a black light.
I can’t say for sure (having never tried it) how much of it holds up after actually being washed but back in college a lot of people would paint their walls (usually graffiti style) with detergent and then during parties they would turn on black lights. The rest of the time you couldn’t tell anything was out of the ordinary.
I’ve often wondered how many of those stains would just be left over laundry detergent residue.
Would it remain as transparent after being rubbed off?
According to the thread I linked to in post 3, it’s phosphorus. I can neither confirm nor deny.
This is the source of the “whiter than white” in old laundry commercials. The detergent would glow in UV (hence in sunlight). Not enough to be noticeable, but enough to add that extra brightness.
In high school we had a play where we used a fairly hefty black light in one sequence (IIRC, about 4 or 8 of the 3-foot flourescent tubes). Not only did fresh white clothing glow in the purplish glow, but so did teeth. Of course this was well before Basic Instinct, so even teenage minds did not make the inappropriate inference. And, I don’t recall any unexplained glowing stains either.
And I thought of this video. Not sure where I first saw it.
Fluorescence is easily quenched, so it isn’t necessary that the fluorescent component is present in semen but not present in blood.
Ewwwww.
An effect that apparently is hard to reproduce in dentures.