Detecting hidden blood stains in crime scenesIf 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.
Other uses of alternate light sources Indeed, many forms of physical evidence will fluoresce. But modern science has resulted in the development of chemicals that “make” objects fluoresce. When using fluorescent chemicals, latent fingerprint development can be greatly improved. Fluorescent latent print powders have the ability to make the latent residue on a surface fluoresce. The benefit here is that the ridges fluoresce brightly and when photographed, a multi-colored or confused background can be minimized to the point where it does not show up in photographs. Fluorescent liquids are used to develop latent prints on porous surfaces such as paper and cardboard.
Fluorescent dyes are used to enhance latent prints developed using superglue fuming. The use of alternate light sources provides a highly practical and efficient means of locating physical evidence at crime scenes. The invention and perfection of Light Emitting Diodes (LEDs) has further advanced evidence recovery since even 1 and 3 watt LEDs can be installed in small, hand-held flashlights, and their performance is remarkable.
http://www.crime-scene-investigator.net/print/alternatelightsources-print.htmleta. Sorry just noticed davel posted a snippet from this already.