What Does UV Light Detect?

UV light is used to detect the presence of trace evidence in forensic investigations.

Blood, urine, semen and saliva can present visible fluorescence.

UV or black light reveals changes on the surface of objects as it causes specific fluorescence in materials depending on composition and age.

Can UV light detect sperm?

The same holds for many organic substances, and most bodily fluids—including sweat, saliva, and urine—will shine when you put them under an ultraviolet “black light.” Criminal investigators use black lights to detect semen because they’re portable and easy to use.

Why do things glow under UV light?

Phosphors are substances that emit visible light in response to radiation. Phosphors hit by UV light become excited and naturally fluoresce, or in other words, glow. For example, your teeth and fingernails contain phosphors, which explains why they glow under a black light.

What shows up under a blacklight?

Biological Fluids

Beneath a black light, blood turns black, unless sprayed with luminol which gives it a blue-glow. Saliva, semen and urine also glow when hit with a black light. Most biological fluids contain fluorescent molecules to help them glow.

What is the difference between a black light and an ultraviolet light?

Difference Between Black Light & UV Light. Strictly speaking, a black light is a kind of UV light. Black lights emit ultraviolet radiation (UV light). UV is radiation with a wavelength just shorter than that of violet light, which is the shortest wavelength of light in the visible part of the electromagnetic spectrum.