Risks, Myths, and Basics of UV-C Light

Most people have a basic knowledge of ultraviolet (UV) light from tanning and vitamin d benefits as well as drawbacks from overexposure that can lead to sunburns or eye irritations without proper protection like sunscreen or sun glasses.

What is less well-known is that UVC light is an old disinfection technology used for decades in water treatment, health care, and food processing.

In recent years, it has been gaining traction and acceptance for broader use everyday life because of its inherent powerful "anti-germ" properties and that it's totally chemical free.

From public transportation to offices and homes, UVC is being integrated as a way to mitigate transmission risks on high-traffic and high-touch surfaces for viruses and germs.


The resurgence of this technology has also brought some new myths.

This 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 right safety precautions, UVC light is safe.

It could be argued that in the long run, it is safer than many other disinfectants because it doesn’t leave chemicals behind on the surfaces it cleans.

However, it is important to understand how it works and what safety precautions are required to use it safely. 

The Basics of Ultraviolet Light

To better understand the health effects of UVC on the body, it’s important to understand what it is and how it is generated.  

UV is light in the form of energy that is emitted from the sun.

It falls within the electromagnetic spectrum into 3 categories with different wavelengths and properties.

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

Source: Once Lighting – The Full Light Spectrum

Both UVA and UVB rays contribute to Vitamin D synthesis and tanning of the skin.

Over exposure from these rays is responsible for the sunburn you receive after falling asleep outside on a summer's day at the beach.

It's widely accepted that a lifetime of exposure to UVB is linked to cancer and prolonged repetitive exposure leads to lasting skin damage.

UVC is quite different from the other two UV categories.

Like visible light, UVC follows the physics of inverse-square law. UVC intensity from the emanating source drops by 1 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 that 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

Similar to UVB light from the sun, exposure to UVC can cause temporary skin and eye damage (photokeratitis) when they are exposed, typically after 6-12 hours of consistent exposure to the eyes.

The dosage or energy a person receives depends on the strength of the light, the length of time the skin is exposed and whether the skin is covered with clothing.

UV-C exposure 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.

It's recommended to wearing protective eye-wear rated for UVC and follow guidelines. The right eye-wear can block out 100% of the UV-C light against the eyes.

Serious injuries from UVC exposure usually resolve within a week with no known long-term damage.”[6]

However, the three categories do not pose the same risks, or even the same benefits.

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 a 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 attributed mostly to the shorter UVB wavelength rather than the UVA light.(7)

UVC, specifically 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.

While UVA and UVB wavelengths are not effective as cleaners, UVC is incredibly effective at killing viruses and germs. 



The discussions about UV light has led to myths about its use. Let’s debunk the most egregious myths. 

Myth: UVC germicidal properties can penetrate through glass. 

UV-C can't pass through 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, it's below the visible spectrum of light.

UV-C light only bounces on a few materials, such as aluminum. Most surfaces will absorb the light completely, even glass.

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.

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

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 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 a pathogen

Smart UV's testing 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 whence this myth derives because it is in contradiction to the other myths. UVC is more effective than a lot of current cleaning products without the residual risks.

Fennelly (2020) details the risks posed by aerosol transmission, leaving residual contaminants on surfaces.

The FDA details how UVC is an effective method of disinfecting surfaces with minimal risks to those who regularly use potentially contaminated surfaces following application of the UVC on those surfaces. 

UVC Safety and Protection

UV radiation is easily absorbed by glass, plastics, and clothing. Once absorbed UVC is no longer active.

We recommend all operators to wear protective glasses when using UV-C, this mitigates a lot of the risk very well.

UVC light can create a health and safety hazard to the eyes and skin if lamps are improperly used.

However within a controlled environment UVC disinfection can be very safe.

To ensure safe usage operators and staff need to be properly educated, trained and informed regarding the hazards of UVC and follow appropriate precautions.

UVC appliances should only be used in unoccupied rooms, spaces or areas during the entire disinfection cycle (without people, pets or plants present).

To reduce the accidental risk of exposure Smart UV has implemented motion sensors, delayed timers, remote control and protective eyewear.

When deciding on any kind of UVC system to incorporate into a sanitation regimen check for these kinds of safe-guards installed for your safety and to prevent accidental exposure.

Since there are risks with using UVC, it is important to establish an understand, or training process for anyone who will be to using it.

To ensure that this highly effective cleaning method is used with minimal risks, training should be mandatory both prior to use and annually as a refresher course in 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.