Effects of UVc Light

Thread Starter

MrAl

Joined Jun 17, 2014
7,656
Hello there,

I recently obtained a somewhat higher power UVc LED light bulb that really lights up the whole room. My intended use is for disinfecting.

Now i have read on the web that it may hurt your eyes and skin. but i never found any specific data.
For example, 10 watts per square meter over a period of 24 hours.
Nothing like that for either eyes or skin.

Also, no data for killing an average bacterium. Nothing like 20 watts per square meter for 10 minutes, but i have found one that says that bacteria is killed after 10 seconds under a UVc lamp, but again no specs on the lamp.

So anyone here ever find any REAL hard data on this subject?

Thanks.
 

bertus

Joined Apr 5, 2008
20,564
Hello,

Perhaps this will answer your question:
Wattage is important if your goal is to sanitize larger areas. If you are just shooting for object disinfection, a 7 or 11 watt wand used within a few inches of the object should be sufficient. Be sure to read the product’s specifications before purchase. And again, make sure you aren’t buying a black light. We found many misleading products claiming to sanitize that were black lights and not UVC emitting lights. Again, ensure that the product description specifically states the nonometers (wavelengths) the light emits.

And this:
What Type Of Coverage Will Different Watt Bulbs Or Lamps Provide?
A 15 watt light bulb will cover approximately 100 square feet.
A 30 watt light bulb will cover approximately 200 square feet.
A 60 watt light bulb will cover approximately 400 square feet.
How Long Will It Take To Sanitize A Room, Object, Or Surface?
The required time for killing different species/microorganisms varies due to their size and shape, how powerful the light or lamp is, how close the surface is to the light rays, and how long they are exposed. Follow the manufacturer’s recommendations related to distance and surface exposure time. For a typical 60 watt light bulb:
  • 5 minutes for objects or surfaces within 3-4 feet of the light, such as masks, countertops, cups, bottles, cell phones, clothing, etc
  • 5 minutes to treat the air in a 50 square foot room
  • 15 minutes to treat the air in a 200 square foot room
  • 30-60 minutes to treat the air in a 400 square foot room

Found on this page:
https://soeasilydistracted.com/home/using-uvc-light-to-sterilize-and-disinfect-bacteria-viruses-and-mold/

Bertus
 

Thread Starter

MrAl

Joined Jun 17, 2014
7,656
Hello,

Perhaps this will answer your question:
Wattage is important if your goal is to sanitize larger areas. If you are just shooting for object disinfection, a 7 or 11 watt wand used within a few inches of the object should be sufficient. Be sure to read the product’s specifications before purchase. And again, make sure you aren’t buying a black light. We found many misleading products claiming to sanitize that were black lights and not UVC emitting lights. Again, ensure that the product description specifically states the nonometers (wavelengths) the light emits.

And this:
What Type Of Coverage Will Different Watt Bulbs Or Lamps Provide?
A 15 watt light bulb will cover approximately 100 square feet.
A 30 watt light bulb will cover approximately 200 square feet.
A 60 watt light bulb will cover approximately 400 square feet.
How Long Will It Take To Sanitize A Room, Object, Or Surface?
The required time for killing different species/microorganisms varies due to their size and shape, how powerful the light or lamp is, how close the surface is to the light rays, and how long they are exposed. Follow the manufacturer’s recommendations related to distance and surface exposure time. For a typical 60 watt light bulb:
  • 5 minutes for objects or surfaces within 3-4 feet of the light, such as masks, countertops, cups, bottles, cell phones, clothing, etc
  • 5 minutes to treat the air in a 50 square foot room
  • 15 minutes to treat the air in a 200 square foot room
  • 30-60 minutes to treat the air in a 400 square foot room

Found on this page:
https://soeasilydistracted.com/home/using-uvc-light-to-sterilize-and-disinfect-bacteria-viruses-and-mold/

Bertus
Hello,

Thanks for the info that is more than what i found. That might serve as a guide.

What i was hoping for was some scientific data that is very precise such as 10 watt minutes per square meter or something like that but i wonder if that exists.
For example, a 50 watt bulb over 50 square feet for 2 minutes would be (very approximately) 2 watt minutes per square foot, although i am simplifying this a lot because we'd really have to take into account the solid angle it makes with say the floor. So it would be in terms of energy per square length unit.
I am beginning to wonder if this kind of data is available anywhere.
What this would mean is i could take any UVc source and square footage and distance and calculate the required exposure time.
One of the problems that comes up is that the manufacturer does not always provide any recommendations.
 

Thread Starter

MrAl

Joined Jun 17, 2014
7,656
Hello again,

Hey i found something that specifies the energy needed to disable the viruses...
https://www.consumerlab.com/answers/does-uv-light-kill-coronavirus/uv-light-covid/


Here is an excerpt...


[START QUOTE]

How UV Light Kills Germs
------------------------

UV radiation kills viruses and bacteria by damaging their genetic material (DNA and RNA). Of the three main types of UV light, UVC (which has a wavelength range of 200 to 280 nm) is the most effective for inactivating viruses, with the most effect wavelength being about 260 nm (Lytle, J Virol 2005).

In order to be effective, the right "dose" of UVC must be applied. The dose is a function of the UVC intensity or "irradiance" from a specific distance from the object times the number of seconds the object is exposed. Irradiance is measured in milliwatts (mW) per square centimeter (cm2), and the dose of UVC is measured in millijoules (mJ) per square centimeter (cm2) of the object being irradiated. (In scientific terms, 1 mWs/cm2 =1 mJ/cm2).

So if your UVC lamp has an irradiance of 5 mW/cm2 at a specified distance from an object, then holding the lamp at that distance from the object for 8 seconds will deliver a dose of 40 mJ/cm2, because 5 mW/cm2 multiplied by 8 seconds = 40 mWs/cm2 or 40 mJ/cm2.

A dose of 40 mJ/ cm2 is generally considered sufficient to disinfect (99.9% reduction in infectivity) a wide range of bacteria and viruses, including certain coronaviruses that infect animals (Malayeri, IUVA News 2016).

Although sunlight does not contain UVC light (because UVC light is filtered by the earth's atmosphere), it may still be very effective against SARS-CoV-2. According to Department of Homeland Security (DHS) documents obtained by Yahoo News and noted in a White House briefing, preliminary tests by government researchers showed that simulated sunlight (equivalent to mid-day sun on a sunny day in the middle latitudes of the U.S.) reduced active SARS-CoV-2 to non-detectable levels after only 3 minutes on a non-porous surface and was similarly effective against the virus in air. Note, however, that this is not instantaneous: If you immediately inhale droplets from a cough or sneeze of an infected person, it won't matter if you are outside on sunny day or indoors. In addition, researchers in China have reported that high temperature and UV radiation do not appear to reduce the transmission of COVID-19 (Yao, Eur Respir J 2020).


What Dose of UVC Light Kills SARS-CoV-2?
----------------------------------------

A laboratory study showed that when pieces of fabric from N95 masks and stainless steel were contaminated with a high concentration of SARS-CoV-2 and then exposed to a large hospital-type UVC lamp (containing a large array of small, LED UVC lamps), it took about one hour for the virus to become undetectable on the mask but just about 12 minutes on steel. The distance from the UVC lamp to the objects was approximately 20 inches (50 cm), at which distance the lamp had an irradiance of just 0.005 mW/cm2 (or 5 microWatts/cm2 or 5 µW/cm2) (Fischer, medRxiv, 2020 — preprint). This means that the effective dose needed to kill the virus to the point of being undetectable on the N95 fabric was 18 mJ/cm2 and, on steel, it was just 3.6 mJ/cm2. Bear in mind, however, that extra time might be needed to disinfect surfaces of larger objects and those with curved surfaces which would require different lamp angles.


[END QUOTE]
 
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