Investigate a crime scene for signs of biological fluids, and do so without destroying any evidence or causing any physical disruption? It sounds like an impossible task. Yet detectives all around the globe are able to do it every day, solving crimes and collecting evidence in the process. How? Simply by shining a specially-filtered light and viewing the results through a pair of forensic glasses.
How Forensic Glasses Work
“Identification of biological evidences, such as blood, semen, saliva, and urine, are important for crime scene investigations,” notes a 2010 report from the Malaysian Journal of Forensic Sciences. “…This method is a simple, presumptive, non-destructive test and applicable for detecting most types of biological evidences. Biological evidences can be detected by forensic light sources due to their natural characteristics, such as light absorption or fluorescence effect.”
So how does this system work? The answer involves just a few simple scientific principles. To start with, know that certain fluids reflect visibly when exposed to X-rays or UV light. The reason is that different substances react (and become visible) at different wavelengths. So a substance that is invisible to the naked eye under “normal” light conditions will suddenly become highly visible when a UV lamp is aimed at it…if you have the right color filter to interpret the necessary wavelength. And that where forensic glasses come into play.
Forensic glasses filter out light from all but the selected wavelength, revealing whatever substance the investigator is searching for. Once the evidence is identified, it can be photographed by a camera equipped with a lens made of the same color as the forensic glasses that spotted it, and samples can be taken for further investigation. Three different filter colors – red, orange, and/or yellow – are typically used for this process, each one designed to reveal a different wavelength. The following chart describes the properties associated with each filter color (wavelengths are measured in nanometers, or “nm” for short):
- A red lens reveals a wavelength that travels at 583nm.
- An orange lens reveals a wavelength that travels at 549nm.
- A yellow lens reveals a wavelength that travels at 480nm.
Forensic glasses, therefore, have become a most valuable tool for investigators and detectives to use when examining a crime scene or any evidence removed from a crime scene. As with any other eyewear, various frame formats are used to accommodate individual preferences or specific crime scene requirements. Phillips forensic glasses are available in nine different styles, some utilizing a wrap-around format while others are designed to fit over prescription eyewear.
Features on the various styles include splash and side protection, adjustable and telescoping temple bars, chemical-resistant lightweight nylon frames, rubber nose pads, and rubberized temple bars. All nine styles are ANSI Z87 safety rated and available with any of the three lens colors described above, offering Phillips Safety customers a total of 27 different choices. If you’re in the market for forensic glasses, you’ve come to the right place.