What is an Alternate Light Source (ALS) used for?

• A. A device that warms samples
• B. A chemical reagent
• C. An invaluable tool when seeking trace evidence of hairs, fibers, fingerprints, and biological stains. By the use of various wave lengths of light
• D. A type of fingerprint powder

Answer: (C)

Alternate Light Source uses different wavelengths of light to reveal evidence that isn’t visible under normal white light. By exciting materials with UV, visible, and near-infrared light and often using filters, certain substances fluoresce or contrast differently, making trace evidence like hairs, fibers, fingerprints, and biological stains come into view. This non-destructive visualization helps locate and document evidence on a variety of surfaces, sometimes enhancing ridge detail in prints or highlighting residual fluids that would otherwise go unseen. It’s not about warming samples, it’s not a chemical reagent, and it isn’t a type of fingerprint powder.