Which option best describes what an Alternate Light Source allows a technician to employ?

• A. Only UV light
• B. Only visible light
• C. Only broad-spectrum light
• D. A variety of narrow wavelengths of the light spectrum to identify, visualize, and document physical evidence

Answer: (D)

Alternate Light Source works by emitting light at specific, narrow wavelengths to excite substances so they fluoresce or luminesce, making traces that are invisible under normal lighting visible against the surface. Because these effects depend on the material, technicians switch among multiple narrow-band wavelengths to optimize detection for different types of evidence—bodily fluids, fibers, residues, or inks—and then document the results with appropriate imaging. This is why the description that emphasizes a variety of narrow wavelengths used to identify, visualize, and document physical evidence is the best fit. Using only UV light, or only visible light, or broad-spectrum light would limit detection and imaging; ALS relies on selecting from several narrow wavelengths to maximize visualization of diverse evidence.