All these years watching several TV cop shows, like, NYPD Blue and Law and Order, seeing them grab this fluorescent blue light lamp on a crime scene to show blood stains, well, I just found out this is not true nor accurate in real life crime investigations. It was invented for our amusement only!
It is interesting to learn this fact from a reliable source, a Criminal Justice Forensic agent retired now: Don Penven
If you watch many of the TV “Cop” shows, you will see at some point those working a crime scene using a blue light in search of invisible blood (blood stains that were cleaned up). Shazam! Blue-white stains appear all over the floors, walls and objects sitting around the crime scene! But in reality—this cannot happen. You see, blood does not fluoresce by applying UV or visible blue light.
Blood, even minute quantities that remain after clean-up, can be made to “luminesce;” that is, by spraying certain chemicals such as Luminol, BlueStar or Fluorescene on the various surfaces, blood will luminesce, or simply “glow in the dark”—and adding blue light is not necessary. So what can alternate light sources reveal? Although blood does not fluoresce, certain other physiological fluids will. UV alternate light sources can reveal the following: seminal fluid, saliva and urine stains. Also, certain narcotics will fluoresce as will bone and teeth fragments.