The one they use to find dirt and stuff left behind like that blue light.
a black light Black Light Stain Detector (Commercial Grade) Professional Ultraviolet Inspection Light Applications Hotel / Motel House Keeping Hospital House Keeping Restaurant Cleaning Food Safety Applications Lab Safety Environments Pet Stains Auto Detailing Gemstone Authensity Art Collectors Antique Verification Law Enforcement Banks
blacklight? UV light / ultraviolet?
