A brief history of germicidal UV light :
2014 outbreak of the Ebola virus and the recent spread of the novel coronavirus disease 2020 (COVID-19) have generated renew interest in germicidal ultraviolet (UV) lamps for disinfection. UV radiant energy was first used for disinfecting surfaces in 1877, then in water since 1910 and in air sterilisation since 1935. Germicidal UV light is being used in many countries to control airborne transmission of tuberculosis. However, most of the public do not aware of its unique value in disinfection of air and contaminated surfaces.
What is germicidal UV light ? It is effective to kill virus and bacteria in the air ?
Germicidal UV (UV) refers to using ultraviolet radiant energy to inactivate bacteria, mold spores, fungi or viruses. Germicidal ultraviolet (UV) is a short-wavelength ultraviolet “light” (radiant energy) that has been shown to kill bacteria and spores and to inactivate viruses. Wavelengths in the photobiological ultraviolet spectral band known as the “UV-C,” from 200 to 280 nanometers (nm). It has been shown to be the most effective for disinfection, although longer, less energetic UV can also disinfect if applied in much greater doses. UV-C wavelengths comprise photons (particles of light) that are the most energetic in the optical spectrum (comprising UV, visible, and infrared) and therefore are the most photochemically active.
UV-C kills living bacteria, but viruses are technically not living organisms; thus, the correct way to term it is “inactivate viruses.” Individual, energetic UV-C photons photochemically interact with the RNA and DNA molecules in a virus or bacterium to render these microbes non-infectious. This all happens on the microscopic level.
What are the impact and effectiveness of 3 types of UV light ; UV-A, UV-B and UV-C ?
UV-A and longer (visible) wavelengths do not have germicidally effective emission wavelengths to inactivate viruses. Their relative disinfection capability is very minimal on the order of 1,000 times less effective than the low-pressure germicidal lamp
UV-B (280 to 315 nm), particularly the shorter wavelengths near 300 nm and below, can be relatively effective as a germicidal source, but in accidental exposures there is a significantly higher risk for severe sunburn and even delayed effects for both skin and eyes, because UV-B penetrates the skin more deeply.
UV-C (200 – 280 nm) as been shown to destroy the outer protein coating of the SARS-Coronavirus, which is a different virus from the current SARS-CoV-2 virus. The destruction ultimately leads to inactivation of the virus. Many publication reported UV-C light could kill 99.9% of airborne coronaviruses in about 25 minutes (see Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses). According to the International Ultraviolet Association, it is generally accepted that 254 nm light will kill at least 99.99% of “any pathogenic microorganism” (see Ultraviolet light fight new virus). Hence, UV-C radiation is found to be most effective compare with UV-B & UV-A to kills living microorganisms; bacteria, mold spores, fungi or viruses. It also has the similar high risk effect like UV-B, when accidental exposures to UV-C, may cause severe sunburn effect for skin and eyes.
On layman term, we can roughly conclude as follow :
- Ultraviolet A (UV-A) has a longer wavelength, however, if expose directly it is associated with skin aging.
- Ultraviolet B (UV-B) has a shorter wavelength, however, if expose directly it is associated with skin burning.
- Ultraviolet C (UV-C) has a shortest wavelength, It is most effective to inactivate bacteria, virus, spores and fungi.
UV light (A, B, & C) while differ in how they affect the skin, they all do harm. Unprotected exposure to UV-A, UV-B and UV-C damages the DNA in skin cells, producing genetic defects, or mutations, that can lead to skin cancer (as well as premature aging). These rays can also cause eye damage, including cataracts and eyelid cancers.
Why are the effective ways to implementing Air UV steriliser ?
Obviously, the germicidal UV light is UV-C, typically around 254 nm wavelength. In order for UV-C to inactivate viruses, bacteria, spores and fungi, these microorganisms have to be exposed directly under the radiation. Inactivation of viruses on surfaces may not be effective if there is blockage of the UV radiation by soil, such as dust, or other contaminants such as bodily fluids.
Secondly, the dose, duration and area of exposure are also important for the UV-C radiation to be effective. Example, if the UV-C lamp has low does, it may need to take longer exposure to a given area to potentially provide effective inactivation of bacteria and viruses.
Thirdly, due the health impact and risk of UV-C light, it is best to be employed inside a close chamber or air ducts to disinfect the air. This is the safest way to employ the UV-C radiation because direct UV-C exposure to human skin or eyes may cause injuries and cancer. Whilst it is also a lost of productivity, when you implement the UV-C air steriliser in a workplace and no human is allow to present inside. Furthermore, the direct exposure of UV-C to furniture’s surface and building material, especially polymers could cause alteration in colour and deterioration of materials.
Please see the comparison of these two types of UV light Air Steriliser
(1) The low dose home UV light air steriliser
(2) The high efficient UV light air steriliser
The proper UV light Air Steriliser must fulfil following criteria :
- No direct exposure to human skin and eyes
- Implement for longer duration, 24/7
- Optimised UV dose and area of exposure
- Low energy consumption
- Quiet, < 60 dBa
- Long life span of UV-C light lamp, 9000 – 12000 hours
- Come with pre-filter at the inlet and outlet of UV-C light chamber, to prevent reduction of UV-C effectiveness due to dust
The UV-C Air Steriliser we recommended are HySafe Air & HySafe Air Eco. They fulfill all the criteria mentioned above.
Reference :
- https://www.fda.gov/medical-devices/coronavirus-covid-19-and-medical-devices/uv-lights-and-lamps-ultraviolet-c-radiation-disinfection-and-coronavirus
- https://www.skincancer.org/risk-factors/uv-radiation/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4320144/
- https://media.ies.org/docs/standards/IES-CR-2-20-V1-6d.pdf
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7319933/
