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How Long Does It Take for UV Light to Kill Bacteria?

How Long Does It Take for UV Light to Kill Bacteria?

Ultraviolet (UV) light was first discovered in the mid-20th century, introducing a new way for people to eliminate viruses and bacteria. Although UV technology has risen to prominence in recent years, especially during the current COVID-19 pandemic, the majority of the general public does not fully understand exactly how UV lighting helps  kill viruses and bacteria. The following article will shed light (pun intended) on how UV light works, what UV-C products and equipment are available on the market, and the precautions that need to be taken to avoid exposure to human skin.

UV light is divided into several ranges: UV-A, UV-B, UV-C (close to the visible light range) and Vacuum-UV (close to the x-ray range). The UV-C light range is the only one able to destroy germs. It is found in UV water purifiers, used in fish tanks, and in portable UV light sanitizers designed to destroy germs that may exist on your tech gadgets and other regular household items. UV-C light can fracture the molecular bonds of the viruses’ and bacteria’s DNA, affecting their ability to reproduce and ultimately killing them.

UV light is one of the seven sections that make up the electromagnetic spectrum. Lower frequencies are radio waves, microwaves, and infrared (IR). These are harmless to humans and animals. A mid-range frequency that many are familiar with is visible light. Ultraviolet (UV), X-rays, and gamma-rays are the highest frequencies and can be very harmful to humans if used without implementing appropriate safety measures.

As mentioned above, the 3 major types of UV radiation are UV-A, UV-B, and UV-C. UV-C rays can effectively eliminate bacteria and viruses as they have the shortest wavelength of the 3 major UV rays. Their short wavelength of 200 - 400 nanometers (nm) means that they have the highest energy, allowing them to kill deadly pathogens. How does UV radiation primarily kill microbes? UV-C light fractures the molecular bonds of the viruses and damages the DNA of microbes and bacteria, affecting their ability to reproduce and ultimately killing them. It has also been known to destroy “superbugs”, whose resistance to antibiotics makes them notoriously hard to eliminate. The efficacy of UV-C lighting has seen many people look to it as a means to kill the coronavirus by decontaminating surfaces and objects on which the virus may be present.

Studies conducted by researchers at John Hopkins University using UV light on “high touch” public spaces in hospitals such as  bed rails, tray tables, and vitals monitors have revealed that it only takes 15 minutes for these objects to be disinfected using UV light. Remarkably, the study revealed 25 out of 27 high-touch surfaces used in the study were devoid of any bacteria after being exposed to UV light. To destroy bacteria, ultraviolet radiation is used as a disinfectant by utilizing a 200 to 300 nanometre range. To eradicate a virus, extremely high levels of UV light would be required and the amount of UV required and the time needed would be dependent on many factors, such as the shape  and  type of material that the virus is found on. Current UV devices are insufficient to adequately kill viruses. Efforts are being made to create a portable UV device that is capable of releasing high-intensity rays able to kill viruses, such as the SARS-CoV-2 virus.

UV-C lights are available to consumers in a variety of different products including UV-C lamps and wands. The length of time needed to destroy viruses and bacteria is unique to each device. Each UV-C device will state on the packaging or the packaging insert how long it will take to sanitize the product and how close the object will need to be held to the device. UV light is only effective on smooth, flat surfaces and cannot effectively disinfect rounded objects such as the buttons of a remote control, nor can it get into crevices. Other forms of disinfection would be required to adequately clean these objects.

A virus’s exposure to radiation is believed to subdue cell-mediated immunity, which may affect the course of a viral infection. As previously mentioned, UV-C possesses the ability to critically destroy a virus’s molecular bonds, inhibiting the virus from multiplying and becoming a threat to humans. Sunlight, particularly UV radiation, is the main natural virucide that exists in our environment. UV radiation destroys viruses by chemically changing their genetic makeup. The most efficient wavelength to bring about inactivation is 260nm. The nucleic acids within viruses can be harmed by UV-A and UV-B radiation, however, they are not as effective and potent as UV-C.

The growing popularity of UV radiation has seen it being used in a variety of products such as UV germicidal lamps, and water filters. Recent developments have helped to place UV technology in portable wands that may be easily transported. Because of this, it is being used in a variety of environments, from hospitals to  households. The large variety of objects that UV products can disinfect include, but are not limited to: surfaces, paper goods, water, air, toys, household objects, tech devices, and even fresh produce.

Not all UV-C products being advertised are genuine, therefore it is important to do sufficient research before committing to buying a specific product. Counterfeiters are looking to make a quick dollar at a time when UV-C product sales are soaring. Ensure that you have purchased your product from a reputable source. This can be done by checking the reviews of the product that you are intending to buy and doing a quick search of the company online to ensure their credibility. 

To determine whether or not a UV light is working properly:

  • Hold a white object up to the light - UV light will clearly irradiate color found on the violet spectrum. However, this cannot be seen by the naked eye. In order to see this violet color, an object lacking in pigment needs to be held up to the light such as a white piece of paper or a sock.
  • Closely monitor the item - If the majority of the item turns a violet shade, it means that the UV bulb is functioning the way it is meant to. If the object is still largely white, this might mean that the UV bulb is defective.
  • If you remain unsure - Move the bulb to another light fixture and repeat the test. If the test fails the second time around, you are most likely dealing with a defective or fake UV light.
  • The correct safety precautions must be taken when handling UV radiation, specifically UV-C as it is the strongest form of ultraviolet radiation. Overexposure to UV-C may cause sunburn or even skin cancer. After purchasing a UV-C product, make sure that it is installed and configured in a way that blocks exposure of the rays to any humans and animals. Stringent safety measures are particularly important as UV-C rays are invisible which increases the chance of accidental exposure. Materials and objects that may be present in the home and workplace such as houseplants, wood, and plastic may be damaged from accidental exposure to UV radiation.

    UV radiation as a form of disinfection has been steadily growing in popularity. Its appeal lies in its efficacy when used correctly, and in the portability of the increasing number of UV-C products that are becoming available. Always remember to implement the correct safety measures as UV-C rays can be extremely harmful to humans, animals, and objects. UV radiation is an exciting technology that, if harnessed correctly, may make our world a safer and cleaner place.

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