Does UV Light Kill Bacteria?

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Written By Jamila W.
UV light disinfection

If the COVID-19 outbreak taught us anything, it’s that bacteria and viruses are all around us – and they can be notoriously hard to kill.

You can regularly clean and disinfect household surfaces – doorknobs, countertops, and other high-touch areas throughout your home – and wash your hands with antibacterial soap. But what about the air you breathe?

Sure, they’re invisible to the naked eye, but make no mistake; viruses, bacteria, and fungi are present everywhere – including the air you’re breathing right now.

Here’s an eye-opening fact for you:

Every time you take a breath, you’re inhaling tens of thousands of microorganisms. According to some reports, each breath of air contains at least 5,000 viruses, 10,000 bacteria, and, to make matters even worse, one or two species of “invisible” fungi. And if you consider that the average respiratory rate for adults is 12 to 20 per minute, it becomes painfully apparent how important indoor air quality is.

But what can you do about the viruses and bacteria floating in the air? Does UV light kill bacteria

Yes, numerous studies have confirmed the effectiveness of ultraviolet germicidal irradiation. In fact, healthcare institutions have been using UV technology as a means of disinfection for years now.

Stick around, and learn more about how UV light can help keep your home germ-free.

UV Light 101: An Introduction To Different Types Of UV Light

When you think “UV radiation,” your mind probably goes straight to UV-A or UV-B rays. That’s understandable; these are the most commonly talked about types of UV light since they are the ones responsible for premature skin aging, sunburns, and skin cancers. However, not many people realize that there’s actually a third type of UV light, known as UV-C light. 

That’s why we’ll start with a quick overview of the three primary types of UV radiation

  • UV-A rays have the longest wavelength in the solar spectrum and are defined as ultraviolet (UV) radiation within the wavelength range of 315 to 400 nanometers. 
  • UV-B rays are defined as ultraviolet (UV) radiation within the wavelength range of 280 to 315 nanometers. 
  • UV-C rays have the shortest wavelength – and, consequently, the highest energy – and are defined as ultraviolet radiation within the wavelength range of 100 to 280 nanometers.

Do note that when we talk about UV disinfection, we are not implying that direct exposure to sunlight would be enough to kill germs. Instead, we are referring to the ability of UV-C radiation, in particular, to kill pathogens, including viruses, bacteria, and fungi. That’s where the moniker “germicidal UV” comes from: 

Due to its high-energy, short-wavelength nature, type C electromagnetic radiation can be highly effective at neutralizing germs.

Here’s where things get complicated: 

Unlike UV-A or UV-B rays, which reach our planet’s surface, UV-C rays never actually make it through the Earth’s atmosphere. They are fully absorbed by the ozone layer, meaning we’re not exposed to it naturally. That’s a good thing; it’s the most dangerous type of UV radiation

The same properties that make UV-C light such an efficient germicidal agent also make it potentially carcinogenic to humans, especially in high doses.

Exploring Anti-Bacterial Properties Of UVC Light

Effectiveness of UV system in infection control

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Ultraviolet germicidal irradiation – or, in simple terms, the exposure to UVC radiation as a means of killing germs is not a new concept. We’ve known for decades that there’s a type of ultraviolet light – UVC light, to be specific – that can efficiently eliminate microbes, primarily bacteria, and viruses. In fact, one of the oldest articles on the topic, titled “The Influence of Light Upon the Development of Bacteria,” was published in 1877. That’s more than a hundred years ago, mind you.

However, as we pointed out earlier, the issue with conventional germicidal UVC radiation is that it is a potential health hazard. The FDA warns that even short exposure to direct UVC radiation through human-made sources like UV lamps can lead to eye injuries and skin burns.

Far-UVC Rays & Broad-Spectrum Light

That’s where far-UVC comes to play:

Far-UVC light has a shorter wavelength range – between 207 and 222 nanometers – compared to conventional germicidal UV-C light. This form of narrow-spectrum UV light is not capable of penetrating the outer layers of the skin – but still effectively kills bacteria.

Columbia University scientists remarked on the potential of using far-UVC light as a safe alternative to conventional UVC rays a decade ago. Since then, there have been multiple studies – and all confirmed the far-UVC light’s ability to eliminate bacteria.

The most significant advancement, however, has been the study published in 2022, which found that far-UVC devices can rapidly reduce levels of microbes in indoor air by more than 98%.

That said, some manufacturers, like those powered by Violet Defense Technology, turned their attention to broad-spectrum light instead. Violet Defense Technology has developed patented UV systems that rely on broad-spectrum light – germicidal UV-C, along with UV-A and UV-B rays – and violet-blue light.

How Does UV Light Kill Bacteria?

Ultraviolet germicidal irradiation is based on the principle of transferring electromagnetic energy to the microorganism’s genetic material – DNA and RNA – and breaking down certain chemical bonds within it. So, in simple terms, UVC light will kill germs by disrupting cellular processes and damaging their DNA or RNA; the accumulation of that damage eventually results in cell death.

The UV system emits shortwave electromagnetic radiation. When UV-C radiation penetrates the cell, photon absorption triggers a reaction that forms specific thymine or cytosine dimers in DNA (uracil dimers in RNA). That renders the microbe incapable of replicating and can result in mutations and cell death. And once the microorganism is no longer able to multiply, it becomes harmless and can be considered “dead” in biological terms. 

It’s worth mentioning that violet-blue light, which falls within the wavelength range of 405 to 470 nanometers, works in a slightly different way and is based on the principles of bacterial photoinactivation with visible light.

In essence, exposure to violet-blue light causes photoexcitation of light-sensitive molecules (porphyrins), causing the release of reactive oxygen species (ROS) – highly reactive, oxygen-containing radicals – that are toxic to bacterial cells and can result in cell death.

How Long Does It Take For UV Rays To Kill Bacteria And Viruses?

There is no “one size fits all” answer here. That is to say:

How long it may take for the UV lamp to kill bacteria depends on several factors – the most important being the type of bacteria you’re dealing with. Some microorganisms might be able to resist UV disinfection better than others, requiring prolonged exposure and higher UV dose. 

On that note, the second important factor to consider here is the required UV dose – which, again, depends on the specific type of bacteria you’re targeting. You can calculate the UV dose by multiplying UV intensity by exposure time. Obviously, germicidal UV lamps that boast a higher intensity will be more efficient at killing bacteria than a low-intensity UV system.

UVC Light FAQs

Let’s answer any remaining questions you might have about UV light’s ability to efficiently kill germs in your home.

Q: What are the risks associated with UVC lamps?

According to the FDA, some UV lamps – primarily mercury lamps – can release small doses of UVB rays, making long-term exposure dangerous for the skin. In fact, it increases the risk of skin cancer and cataracts. Besides issues associated with mercury vapor-based lamps, some UVC light systems may produce ozone, leading to irritation of the respiratory system.

Q: Does UV light really sanitize water?

Yes, a UV system can be used for water disinfection. In fact, the treatment of water systems is currently one of the most effective applications of UV technology. Since it doesn’t involve the use of chemicals, UV light disinfection is a great choice for disinfection of drinking water. Don’t forget to take UV transmittance (water’s ability to transmit ultraviolet energy) into account, though. The minimum UVT level for successful water treatment should be 75%.

Q: Does UV light work on all microorganisms?

Yes, a UV system effectively kills bacteria, along with a wide range of other pathogens, such as viruses, protozoa, mold, and fungi. However, the level of UV light exposure required to achieve proper disinfection can vary.

Conclusion

So, does UV light kill bacteria?

The answer is a definite “Yes.” In fact, UV lamps have been successfully used for sterilization in the healthcare system – for hospital rooms and surgical tools, among other things – for decades now and have been found to cut the transmission of some drug-resistant bacteria by as much as 30%.

And when it comes to improving indoor air quality, there is arguably no better option than a UV air purifier that combines PECO (photo-electrochemical oxidation) with HEPA filters for maximum efficiency.

Of course, not all UVC lights are created equal; you’ll find that consumer-grade devices come in different forms and varying levels of effectiveness. Be sure to look for proof of independent third-party testing that confirms the manufacturer’s performance claims, and choose wisely.