Examination of crime scenes using monochromatic light sources (light of one specific wavelength) can assist in locating and identifying potential evidence. This type of examination utilizes the inherent luminescent properties of materials (biological fluids, fibers, latent prints) exposed to monochromatic light to help locate these items. Devices providing monochromatic light at specific wavelengths are referred to as Alternate Light Source (ALS).
The above images show various stains on fabric from various biological fluids (left) and fibers/trace material (right) as seen using the ALS to provide monochromatic light of the correct specific wavelength.
The images below show a shirt as viewed in normal lighting (left) and a semen stain on the pocket (right), just under the logo, as seen using the ALS.