They sort of disappeared however: I never saw one used again until I came here and they had one in our local hospital.
(note: I did tend to work in small rural hospitals not big ones so this might not be true for all hospitals).
Ultraviolet light kills germs. (bacteria, and viruses and even mosquitoes).
The devil of course is in the details: What wavelenght, which lights work best, how intense should the light be, and the benefit/harm ration to nearby human beings.
WebMD says certain UV lights can stop the airborne influenza virus without harming people and is used to sterilize things, but because it might cause skin cancer, it is not advised to be used in public.
Science daily article from 2018 suggests it should be used more often to stop influenza, and that low dose UV lights work:
Continuous low doses of far ultraviolet C (far-UVC) light can kill airborne flu viruses without harming human tissues, according to a new study at the Center for Radiological Research at Columbia University Irving Medical Center (CUIMC). The findings suggest that use of overhead far-UVC light in hospitals, doctors' offices, schools, airports, airplanes, and other public spaces could provide a powerful check on seasonal influenza epidemics, as well as influenza pandemics.
The WHO says: uh oh; wait a minute.
translation: It might give you a sunburn like irritation, or you might develop cataracts. (But hey, it's better to die of Corona virus than risk getting a very curable skin cancer 30 years from now?)
a lot of the use depends on the dosage, of course. But using it to decontaminate surfaces and rooms and closed spaces in buses etc. is already being done.
the UK Mirror says that China is blasting buses with UV light to decontaminate them.
it could also be used to decontaminate airplanes.
this 2010 article discusses the history of using UV light to stop the spread of germs.
it has a lot of technical information (like discussing air movement and dosage and wavelength). The use of UV light started in 1845, when it was noted sunlight decontaminated test tubes. But it wasn't used clinically until the 1930s, when it was used to stop the spread of measles, and later for control of TB spread.
TB is common here, and is one area where UV works and is used, which explains the presence of UV lights on the ceiling and near the doorways in some areas of our local hospital.
why did it's use stop? It didn't always work (humidity lowered it's efficiency) and there were worries about ozone and other problems with the older type lights. Then of course came antibiotics, so the perceived need was less urgent (one reason hand cleaning went down too).
but the presence of antibiotic resistance has caused many hospitals to reintroduce the lights to disinfect rooms
UV has other uses in medicine: Doctors still use small UV lights/flashlights (or a "wood's Light) to identify fungus infections, or with dye to identify eye scratches or ulcer, etc.
Don't have a Wood's light? Wired notes MacGuyver used his cellphone as a "black light" to read secret writing on a wall, and they discuss how to do it with a LED light or cellphone.
but of course, the dosages is too low to be much help in killing germs.
Traditionally, UV lights are flourescent type lightbulbs. Indeed, most fluorescent lights have a coating so they don't emit UV light.
They have been working on LED lights that emit UV light to stop viruses and antibiotic resistant germs.
I have no idea on the dosages or types of lights that you have around your house that could be used for cleaning your bathroom or kitchen surfaces.
But since ordinary LED lights are made not to emit UV light, you aren't going to be saved by keeping on your lights.
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Dilbert's podcast mentions
Balaji Srinivasan: Far UV light kills airborne viruses
the technical paper on hospital infection control can be found HERE.
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