But UV flashlights serve a bigger purpose for law enforcement, as they can actually help reveal evidence that may be hard to find under normal lighting during an investigation. This is possible because UV light can increase contrast and make certain substances stand out when they otherwise may have been missed. UV flashlights work by using ultraviolet wavelengths of light to make both items and residues easier to see. As certain materials receive UV light, they absorb the energy and then emit visible light through a process known as fluorescence. UV flashlights are classified as Alternate Light Sources (ALS), and because of their application, are often used in forensic investigations.