It’s an obvious cheap solution.
I once installed a UV light in my house duct work, because it kills spores which would help my allergies.
UVC is safer than UV, though.
UVC is very harmful compared to UVA and UVB. UVA and UVB are what sunscreen protects you from. The atmosphere prevents harmful amounts of UVC from getting to the ground level fortunately.
UVC can cause tissue damage very fast compared to other UV. UVC is used inside HVAC equipment to prevent microbial growth on the AC coils and sometimes in the condensate pans, and it sanitizes the air some as it passes by the light. UVC can cause eye damage very, very quickly too. But inside an air handler with proper safety interlock devices it posses no danger to humans.
Those handheld UV lights are worthless.