Alternate Light Source (ALS): It is becoming more commonplace for investigators to examine any likely surfaces (doors, doorknobs, windows, railings, etc.) with an alternate light source.
These are laser or LED devices that emit a particular wavelength, or spectrum, of light.
Some devices have different filters to provide a variety of spectra that can be photographed or further processed with powders or dye stains.
For example, investigators may use a blue light with an orange filter to find latent prints on desks, chairs, computer equipment or other objects at the scene of a break-in.