Where does UV-C light come from?
Sunlight consists of different kinds of ultraviolet radiation, also known as UV (Figure 1). UV radiation is an electromagnetic radiation just outside the electromagnetic spectrum, making it invisible to the human eye. This type of radiation comes in wavelengths ranging from 100 to 400 nanometres. It is subdivided into three categories by wavelength:
- UV-A; wavelength 315 - 400 nm
- UV-B; wavelength of 280 - 315 nm
- UV-C; wavelength from 100 - 280 nm
Figure 1: UV-C light is blocked by the ozone layer
Different types of radiation have different properties, depending on their wavelength. UV-A reaches the earth’s surface, largely passes through glass and clothing and causes one’s skin to age.
UV-B is another type of radiation that reaches the Earth’s surface. You might think that B stands for ‘brown’, because it makes you tan or burn. Then there is UV-C, which is blocked by the atmosphere and does not reach the Earth. This is just as well, because this type of radiation has a large amount of energy and can be very harmful to humans when they are directly exposed to it.² UV-C light can be generated with the help of special lamps such as LEDs and fluorescent lamps.
What is the effect of UV-C light?
As wavelengths become shorter (as with UV-C), the light contains a greater amount of energy.¹ This energy can damage the DNA and RNA of viruses and bacteria. Some wavelengths of UV light work better than others for inactivating viruses. For example, wavelengths in the UV-C range are particularly damaging to cells because they are taken up by nucleic acids and proteins. Germ-killing effectiveness ranges from 200 nanometers to 300 nanometers, peaking at 250-265 nm.
UV-C light is effective against organisms because it directly attacks DNA & RNA. Thymine, cytosine, adenine and guanine make up the basic components of DNA (see Figure 2). When DNA comes into contact with UV light, a chemical compound is formed that causes the thymine to dimerize, meaning they grow together.
The deadly effect of UC rays is mainly due to the structural defects they cause when thymine dimers are formed. If enough of these dimers are made in the DNA, the DNA replication process is disrupted and the cell cannot replicate.
It does not remove the cells, but it kills the organisms and prevents them from reproducing. This also prevents organisms from becoming resistant to UV-C light. In combination with the right factors, UV-C light is very effective at killing germs, and it can achieve a high log reduction across the spectrum of pathogenic micro-organisms.
Would you like to know how UV-C light is used? Be sure to read this article.
- Rob Reddick. (2021). Type of ultraviolet light most effective at killing coronavirus is also the safest to use around people. Retrieved from: https://theconversation.com/type-of-ultraviolet-light-most-effective-at-killing-coronavirus-is-also-the-safest-to-use-around-people-169602
- Honeywell. (2000). Tech Lit Documents. Consulted from: https://customer.honeywell.com/resources/techlit/TechLitDocuments/50-0000s/50-8788.pdf
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