Risks, Myths, and Basics of UV-C Light

Recently UV-C light has been gaining acceptance for broader commercial and retail use because of its inherent powerful "anti-germ" properties.

You may have seen UVC technology-related news reports from a variety of businesses incorporating this emerging technology.

For example, Smart UV has served customers in the healthcare, academic, and government sectors.

Additionally, we have worked with customers representing the restaurants, hospitality, and fitness industries too. Click here to see some of our client case studies.

The resurgence of this technology has created some new myths.

With the adoption of artificial ultraviolet light use, there has been an increase in myths associated with UV-C. In this article, we will attempt to shed some light on some of these reoccurring misconceptions.

UVC popularity has led to two primary questions: 

  • Is it safe to wield this powerful technology for public use?
  • What is its biological effect on the human body if exposed?

The short answer to the first question is yes, with the proper safety precautions, UVC light can be used safely. Comparatively, in the long-term, we could propose that UV-C is safer than many other disinfectants because it is chemical-free(chemical myth here).

However, it is essential to understand how UVC works, the science behind UVC, and be aware of the safety precautions. We will discuss safe use later (click here if you can't wait). For now, let's jump into what is ultraviolet light and biological exposure.

The Basics of Ultraviolet Light

To better understand the health effects of UVC on the body, it's essential to understand what Ultraviolet light is and how it is generated.  

The sun emits light in the form of energy called Ultraviolet light(UV).

UV falls within the electromagnetic spectrum divided into three categories with different wavelengths and properties.

  1. UVA light ranges between 400nm to 315nm along the electromagnetic spectrum. 95-97% of the UV rays from the sun that reach the ground are UVA rays. 
  2. UVB light ranges from 315nm to 280nm in the electromagnetic spectrum; 3-5% of UV rays from the sun that reaches the ground are UVB rays.
  3. UVC light ranges from 280nm to 100nm and is entirely absorbed by our planet's upper atmosphere, protecting us from any exposure. So the only UVC rays emitted on our planet's surface are from artificial sources such as UVC Lamps.

    Source: Once Lighting – The Full Light Spectrum

    Beneficial Biological effects of UV-A & UV-B 

    Most people have a basic understanding of the positive associated health effects of ultraviolet light (sunlight) exposure. Other than leaving us with a nice tan, the most significant benefit is stimulating our body to produce vitamin D naturally.

    This hormone is also integral in fortifying and managing our body's bone health and regulating thousands of genes that depend on vitamin-D levels in the blood to function.

    You can check out the Environmental Health Perspective's article Benefits of Sunlight to find even more reasons to get acquainted with the sun.

    How much is too much sun?

    The answer is different for everyone. Factors like age, health, clothing worn, skin melanin pigment, and sunscreen can all influence damage received to the skin from UVA and UVB rays.

    We are aware that cumulative excessive exposure to ultraviolet light over a lifetime can increase one's risk for skin cancer, and short-term exposure can result in painful sunburns. But do the risks outweigh the benefits?

    The World Health Organization found in their assessment of disease linked to ultraviolet light that UV exposure only accounts for 0.1% of the total burden of disease measured in disability-adjusted life years(DALYs). DALYS measures how a person's healthy life expectancy is reduced by premature death on disability caused by infection.

    Interestingly, the same report proposed a significantly greater annual burden worldwide for vitamin-D deficiency diseases caused by insufficient UV exposure like cancer and significant autoimmune and musculoskeletal disorders. If you are curious about this report, click this link here.

    So it could be suggested the benefits of exposure to the sun do outweigh the risk. Protection from the sun is essential, but so is sun exposure to maintain healthy vitamin-D levels in the body. If you live in a climate with seasonal cycles, you can always supplement with Vitamin D.

    What about UV-C?

    UVC is quite different from the other two UV categories. For one, as mentioned previously, it is only produced artificially on the surface of our planet. UV-C emitted from the sun is blocked by the ozone layer.

    Although similar to visible light, UVC follows the physics of inverse-square law. UVC intensity from the emanating source drops by one over distance squared and eventually decreases exponentially the further away a person is from the source.

    In other words, the further away a person is from the UVC source, the smaller the dosage they receive. Additionally, the absorption of UVC rays in human skin is minute. So almost no UVC light can reach the living cells in the epidermal layer, so all absorption happens on the dead, cellular layer of the skin.

    The Associated Risks with UV Light

    Like UVB light from the sun, exposure to UVC can cause temporary skin and eye damage (photokeratitis) when exposed, typically after 6-12 hours of consistent exposure to the eyes. The dosage (energy received) depends on the strength, duration of skin exposure, and whether clothing covers the skin.

    UV-C exposure is unlikely to cause acute or long-term damage to the skin but can cause damage to the eye because the eye does not have an outer, dead, protective layer like the skin leaving it susceptible to all forms of UV light. That is why it's best to avoid long direct skin exposure to UVC light, and you should avoid looking into the UVC light source, even briefly.

    UV-C disinfectant appliances should always be used in empty rooms or areas with no one present during operation. Smart UV recommends wearing protective eyewear rated for UVC and following guidelines outlined in the manual. The proper eyewear can block out 100% of the UV-C light from the eyes. Serious injuries from UVC exposure usually resolve within a week with no known long-term damage." [6]

    Now that we know what a better understanding of ultraviolet light and UV-C is let's debunk some common myths about this technology.

    Myth: UVA, UVB, and UVC have equal Germicidal properties?

    UVA light is the longest ultraviolet wavelength that is approximately 1,000 times less effective than UVC at disinfecting. UV energy output is inversely correlated with length along the electromagnetic spectrum, so, generally, the shorter the wavelength, the more energy output associated with it.  

    When the UV weather index is at the peak of 10 on a hot clear day, sun rays can kill some bacteria with 99.9% (Log3) effectiveness in under an hour. This can be mainly attributed to the shorter UVB wavelength rather than the UVA light. (7)

    UVC, precisely 253.7nm, is coined germicidal UV because this short wave spectrum has been proven to be strongly absorbed by microorganisms' DNA, leaving them destroyed on a sub-cellular level which inhibits their pathogenic traits. 

    So UVA and UVB wavelengths do exhibit some germicidal properties (mainly UVB). They are not effective as cleaners or comparable to UVC's incredibly effective germicidal properties. 


    Source : HOW DOES UVC WORK?

    Myth: UVC germicidal properties can penetrate through glass. 

    UV-C can't pass through the typical glass and is absorbed by glass, plastics, and clothes. Once UVC is absorbed, it is no longer active.

    At first glance, this can be surprising because the blue light we see from germicidal lamps is bright and visible. We have to remember that we can't see the germicidal disinfecting light below the visible spectrum.The blue light emitted from the UVC source is safe and is visible light leakage.

    UV-C light only bounces on a few materials, such as aluminum. You'll see the blue light pass through the glass, but the UV-C is stuck behind, making it safe to look at a UV-C lamp from behind the glass. So it's important to remember most surfaces will absorb the light completely, even glass. 

    Myth: UVC creates microbial resistance that result in superbugs like antibiotics

    UVC does not increase microbial resistance.

    UVC does not increase microbial resistance. There is no immunity build-up when germs are exposed to UVC, and there hasn't been for the decades that it has been used. Hospitals care for immunocompromised populations every day by disinfecting their facilities' air and surfaces with medical-grade UVC devices.

    UVC in this setting promotes a safe environment for patients to regain their vitality and regain a healthy immune system that does not diminish or harm their health. No chemical residue is present after a disinfectant cycle finishes, and UVC aids in the fight against superbugs prevalent in healthcare. "A large randomized trial led by Duke Health and published in The Lancet finds the use of UVC machines can cut transmission of four major superbugs by a cumulative 30 percent." (5)

    Myth: UVC does not disinfect viruses because it is not powerful enough.

    Testing of Smart UVs Apollo against pathogens is made to be transparent, interpretable, and accessible for you. To see our summaries for all our lab testing, you can check out our technology page here https://www.smartuv.shop/pages/technology

    It is unclear from where this myth derives because it is in contradiction to the other myths. UVC is more effective than disinfectant products without the residual risks that come with cumulative chemical exposure.

    Fennelly (2020) details the risks posed by aerosol transmission, leaving residual contaminants on surfaces. (link here) The FDA describes how UVC is an effective method of disinfecting surfaces with minimal risks to those who regularly use potentially contaminated surfaces.

    UVC Safety and Protection


    As stated before, UVC appliances should only be used in unoccupied rooms, spaces, or areas during the entire disinfection cycle (without people, pets, or plants present). Motion sensors, delayed timers, remote control, and protective eyewear have been implemented to reduce the risk of exposure. 

    We recommend all operators wear protective glasses when using UV-C. This mitigates a lot of the risk very well. However, UVC light can create a health and safety hazard to the eyes and skin if lamps are improperly used.

    To ensure safe usage, operators and staff need to be adequately educated, trained, and informed regarding the hazards of UVC and follow appropriate precautions. Following these steps will create a controlled environment, which can be very safe for UVC disinfection use.

    Since there are risks with using UVC, it is essential to establish an understanding and training process for anyone who will be to operating the appliance. To ensure that this highly effective cleaning method is used with minimal risks, training should be mandatory both before use and annually as a refresher in the proper handling of the UVC light.


    [1] Branche, C.M. (2009) Environmental control for tuberculosis: Basic upper room ultraviolet germicidal irradiation guidelines for healthcare settings. U.S. Department of Health and Human Services, Centre for Disease Control and Prevention, National Institute for Occupational Safety and Health, NIOSH Publication No. 2009-105.
    [2] Lindsley, W.G. et al (2018) Ambulance disinfection using Ultraviolet Germicidal Irradiation (UVGI): Effects of fixture location and surface reactivity. J. Occup. Environ. Hyg. 15, 1-12.
    [3] Fennelly, K. P (2020) Particle sizes of infectious aerosols: implications for infection control. The Lancet Respiratory Medicine, 15(9), 914-924.
    [4] FDA. (2020) UV Lights and Lamps: Ultraviolet-C Radiation, Disinfection, and Coronavirus. Retrieved February 17, 2021 from
    [5] Duke Health. "UV light can aid hospitals' fight to wipe out drug-resistant superbugs." ScienceDaily. ScienceDaily, 17 January 2017.
    [6] How can different types of ultraviolet radiation affect health?. Ec.europa.eu. 2021 [accessed 2021 Feb 22].
    [7] IES Photobiology Committee. IES Committee Report: Germicidal Ultraviolet (GUV) – Frequently Asked Q. IES Standards Committee; 2020 [accessed 2021 Feb 22] p. 1-24.
    [8] Lucas, R., McMichael, A., Armstrong, B., & Smith, W. (2008). Estimating the global disease burden due to ultraviolet radiation exposure. Retrieved 4 November 2021, from https://pubmed.ncbi.nlm.nih.gov/18276627/
    [9] Mead, N. (2021). Benefits of Sunlight: A Bright Spot for Human Health. Retrieved 4 November 2021, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2290997/