Germ Killer Light.

Yes very interesting. Would be interested to know what the long term exposure to the effects of far uvc light on school children while under prolonged exposure. particularly if they were to spend more than hour each day under their effects.

One might want to check at the same time, the effects of long term exposure to certain reactionary publications. lol

The original news bulletin from the University of St Andrews  dept physics has slightly more details. And is from May 2020.

Far-UVC lamps that emit at wavelengths around 222nm may be safer because proteins in the skin efficiently absorb this light and provide a natural protective barrier.

Not that sure I'd want my outer proteins doing too much absorbing - sounds like surface tissue damage to me ! I note with some concern that these are results of a computer model of how skin ought to react to various wavelengths, not actual tests on real skin, and there is no mention of eyes, Short UV is not focussed by the eyes lens onto the retina in the way that visible light is, so the laser safety thresholds are higher for UV than for Green for example,  but even so there is a lot of work documenting cornea damage at these wavelengths. I think, given the article is nearly 2 years old,  it is probably proving to be harder in practice than it looked in theory.
Mike.

I am not sure that I would like to be exposed to UVC for any lengthy periods on a regular basis. 

I did some investigation into the effects of exposure to UV radiation when we were considering having mercury arc rectifiers on display to the public.  I have copied an extract from one of the papers that I came across “Ultraviolet (UV) Radiation Safety, April 2005, Compiled by Myung Chul Jo, Environmental Health and Safety, University of Nevada Reno.

 “3.1. UV radiation eye hazards

The cornea and lens are the main areas of the eyes affected by UV radiation.

Various components of the human eye are susceptible to damage arising from

photochemical effects as a result of extended exposure to direct/reflected UV

radiation. The UV wavelength is the determining factor as to which part(s) of the

eye may absorb the radiation and suffer biological affects (see table 1).

Table 1. Absorption of UV wavelengths in the Human Eye

Wavelength                  Cornea            Aqueous          lens      Vitreous

100 nm – 280 nm        100%               0                    0          0

300 nm                        92%                 6%                   2%       0

320 nm                        45%                 16%                 36%     1%

340 nm                        37%                 14%                 48%     1%

360 nm                        34%                12%                 52%     2%

The cornea is like the skin in that it can be "sunburned" by exposure to too much

UV radiation. This is called keratoconjunctivitis (snow blindness or welders flash)

and is a condition where the corneal (epithelial) cells are damaged or destroyed.

This condition usually does not present until 6 to 12 hours following the UV

exposure. Although very painful (often described as having sand in the eyes) this

condition is usually temporary (a few days) because the corneal cells will grow

back. In very severe cases, the cornea may become clouded and corneal

transplants may be needed to restore vision. Exposure to UV-C and UV-B present

risk to the cornea. The lens of the eye is unique in that it is formed early in human

development and is not regenerated should it become damaged. For normal vision,

it is essential that the lens remains clear and transparent. Unfortunately, UV-A

exposure is suspected as a cause of cataracts (clouding of the lens).”

David

Well then, if at all worried, just route the airflow through a system that hides the direct U.V. from view. This should be easily incorporated into things like wall mounted air source heat pump units that blow germs generously around village halls for all to catch.

This nasty situation is also found in large shops at main entrances in the form of warm air curtains.

Does the power/effect of U.V. light diminish as per the inverse square law from source?

www.researchgate.net/.../Visual-propagation-of-light-following-the-inverse-square-law_fig2_320926645

Z.

And that we have been doing for years, both for air and for drinking water from private wells. This short history of UV disinfection suggests the late 1800s as being pretty much the start https://www.uvtglobal.com/what-is-uv-c/the-history-of-uv-c/?v=79cba1185463

Mike.