A lot, actually—mostly things you don't notice day to day. UV shows up in disinfection, manufacturing, medicine, and forensics. The useful kind for killing germs is UV-C (around 254 nm). UV-A is what tans you and makes fluorescent posters glow.

Disinfection

This is the big one. Municipal water plants, hospital HVAC systems, and food-processing lines use UV-C to inactivate bacteria, viruses, and mold spores. Water passes a lamp; air gets forced through a UV chamber. No chlorine taste, no chemical residue—but the light has to actually hit the target, and it only works while it's on.

Medical and industrial

Hospitals use UV robots and built-in lamps to disinfect rooms and equipment. Dermatologists use controlled UV (phototherapy) for psoriasis and similar conditions—different wavelengths, carefully dosed. In industry, high-intensity UV cures inks, adhesives, and coatings instantly on printing presses and assembly lines.

Everyday and specialty uses

UV reveals security features on passports and banknotes. Forensics teams use it to spot bodily fluids and altered documents. Aquarium keepers run UV sterilizers on tank water. Gemologists check stones for fluorescence. Semiconductor fabs use deep UV for chip lithography. Black lights at a club? That's UV-A making white fabric glow.

What about home gadgets?

Phone sanitizers, UV wands, and air purifiers with UV bulbs are real products, but results vary. A small box works if the UV reaches all surfaces. A wand only disinfects what you slow down and point at. None of these replace washing your hands or fixing a mold problem at the source.