UVC Guide

The Ultimate Guide for ultraviolet light and everything else you need to know about UVA, UVB, UVC, side-effects, applications and more.



Ultraviolet, also known as UV light, is a component of the electromagnetic spectrum that falls in the region between visible light and X-Rays. Its wavelength is shorter than that of visible light, but longer than X-rays.

UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. Besides its natural solar source, UV light can be also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights.

Short-wave ultraviolet light damages DNA and sterilizes surfaces with which it comes into contact. For us, humans, suntan and sunburn are the most familiar effects of exposure to UV light, along with an increased risk of skin cancer.

The lower wavelength limit of human vision is conventionally taken as 400 nm, so ultraviolet rays are invisible to humans, although some people can perceive light at slightly shorter wavelengths than this. Insects, birds, and some mammals can see near-UV.


The electromagnetic spectrum of ultraviolet radiation (UVR), defined most broadly as 10–400 nanometers, can be subdivided into a few main ranges or types, and the most relevant ones being UVA, UVB and UVC:

UV rays have different levels of penetration. Although natural UVC is blocked by the atmosphere and doesn't make it to us, man-made UVC only goes as far as the outermost cells of our skin, while UVB only goes as far as the topmost layer of our skin and no further. UVA, however, has the highest penetrating power. It easily gets to the deep layers of our skin.

UVA and UVB are commonly used for curing purposes on adhesives, ink, coatings. You may also use UVA for UV inspection and UV fluorescing, while UVB works for disinfection and sterilization to some extent. However, UVC is the most effective and widely used for disinfection and sterilization, such as water sterilization, surface disinfection, and other sterilization purposes.

UVA, unlike UVB, tans your skin almost immediately if you expose your skin to it, and just like UVB, it promotes wrinkling and skin aging. It also increases the risk of skin cancer development.

Here are UVA, UVB and UVC wavelengths and most common applications:

Ultraviolet C (UVC)
  • Short-wave, germicidal, completely absorbed by the ozone layer and atmosphere
  • Wavelength: 200 to 280 nm
  • Useful for disinfection and sensing applications
Ultraviolet B (UVB)
  • Medium-wave, mostly absorbed by the ozone layer
  • Wavelength: 280 to 315 nm
  • Useful for printing curing and medical applications
Ultraviolet A (UVA or “near UV”)
  • Long-wave, black light, not absorbed by the ozone layer
  • Wavelength: 315 to 400 nm
  • Useful for printing curing, tanning beds, sensing and medical applications


None. UVC and UV-C mean the same thing: ultraviolet light of wave length between 200 to 280nm.

Both UVC and Far-UVC are part of the broad Ultraviolet C light spectrum. The largest difference is most UVC products use 254 nanometer light and most Far-UVC products use 222 nanometer light.

Most traditional UVC products (like low pressure mercury lamps) use energy from the 254 nm wavelength because scientists found it the most effective. UVC LEDs, which are relatively new to the market, are generally 260 to 280 nm. Other products use broad spectrum UV, which is a combination of wavelengths found in UV-A, UV-B, and UV-C ranges.

Researchers started focusing on Far-UVC in the last decade. Far-UVC uses a lower range of wavelengths (between 207 and 222 nm) for disinfection. Most Far-UVC products contain 222 nm light.

Unlike UVC, which can damage the skin and eyes, Far-UVC is safe for skin and eyes. Far-UVC does not penetrate the outer layer of skin or eyes, so it doesn't cause any tissue damage. Because Far-UVC is safe for skin and eyes, Far-UVC products can run constantly. They can work at all times to kill pathogens like viruses and bacteria so you are never starting from ground zero, while UVC products only target germs during a timed cycle when no one is in the room.

One of the biggest downsides of Far-UVC is its slow disinfection properties. While UVC can sterilize things quickly and efficiently, Far-UVC requires constant and prolonged exposure in order to achieve the same effects of UVC as a sterilization method.

Scientists and companies have been studying Far UVC for a relatively short time if compared to the more commonly-used 254 nanometer UVC. Currently, there aren't many Far UVC consumer products in the market. While it's believed that Far UVC exposure is safe to the eyes and skin, studies continue to be made while companies start to design products based on this slightly different type of ultraviolet light.

UVC radiation is a known disinfectant for air, surfaces, objects and water that can help mitigate the risk of acquiring an infection and has been used extensively for more than 40 years.

As evident by multiple research studies and reports, when biological organisms are exposed to deep UV light in the range of 200 nm to 300 nm it is absorbed by DNA, RNA, and proteins. Absorption by proteins can lead to rupture of cell walls and death of the organism. Absorption by DNA or RNA (specifically by thymine bases) is known to cause inactivation of the DNA or RNA double helix strands through the formation of thymine dimers. If enough of these dimers are created in DNA, the DNA replication process is disrupted, and the cell cannot replicate.

In other words, if viruses and bacteria are exposed to a certain amount of UVC light for enough period of time, their cells will be destroyed and will be unable to replicate further, dying as a natural result.

All bacteria and viruses tested to date (many hundreds over the years, including various coronaviruses) respond to UVC disinfection. In laboratory testing, our UVC light sources inactivated 99% of SARS-CoV-2 virus on a surface with an exposure time of 6 seconds. A clear indication that UVC can play a valuable part in your protection strategy.

Standard window glass, according to the International Ultraviolet Association, allows UVA to pass through while almost 100% of the UVB and UVC light is blocked. In other words, while it can be safe to stare at a UVC lamp through a glass or window, it's not recommended to do so.

First and foremost, when not used correctly, UVC sterilizers can be dangerous and damaging to your eyes and skin. While UVC boxes and UVC-equipped vacuums are 100% safe, lamps and portable wands have to be used with great care in order to avoid eye and skin exposure.

Secondly, UVC light is highly directional. This natural characteristic prevents ultraviolet light from penetrating in porous or irregular surfaces. While flat and smooth surfaces can be effectively sanitized by UVC, irregular objects, small gaps or porous surfaces such as rugs or sponges may not completely absorb UV light in its deeper layers, resulting in a superficial and somehow incomplete sanitization of those objects.

For example, if you're using an UVC lamp or wand to sanitize a towel hanging in the toilet, you'll need to hand the towel open wide and flip sides at each sanitization pass. If you don't open it wide and expose both sides, limited parts of the towel fabric will get exposed to UVC light, resulting in a partial sanitization of the object.

This limitation can only be improved by using mirrors, multiple sources of UVC light at once or by moving (or rotating) objects and/or UVC light across several sterilization passes.

The third most important downside of using UVC as a sterilization method is energy consumption and, in some cases, ozone generation. Besides the 254 nm output, some lamps also produce UV at a wavelength of 185 nm, which is well off the peak of germicidal effectiveness. That shorter wavelength causes regular oxygen molecules (O2) to break up and form ozone (O3).

Despite being great in the stratosphere, ozone is a pollutant at ground level. When inhaled in high doses, ozone can damage the lungs. Relatively low amounts can cause chest pain, coughing, shortness of breath and throat irritation. Ozone may also worsen chronic respiratory diseases such as asthma and compromise the ability of the body to fight respiratory infections.

Not all UV lamps result in ozone generation. It all depends on the type of glass used in the lamp. Soft glass or regular quartz glass allow the 185 nm UVC to pass through and generate ozone. But when quartz glass doped with titanium is used, all of the 185 nm UVC is absorbed. That's why you should always look for high-quality products made by established brands.

Because of its highly directional nature, UVC sanitizing requires special attention to how the sanitizing device (e.g. lamp, wand, case) is used. These tips and ideas will help you take full advantage of your UVC sanitizing device, and take full advantage of the benefits of UVC light.

First and foremost, always remember that UVC light propagates in a very directional fashion without doing turns or reaching behind objects. That means, pillows, blankets, vases or any kind of two-sided or three-dimensional object must be flipped or rotated during different sterilization sessions.

Portable Lamps

One approach is to simply change objects position every time UVC light is used. This will make sure UVC light will reach all sides of the objects being exposed to it. It's very important to organize and position all objects in the best way possible before you leave a UVC lamp doing its work. This is especially true in children's bedrooms, where things and toys are commonly piled and jammed around.

When a portable UVC lamp is used, another tip is to change the position of the lamp itself between consecutive sessions. This is important when sanitizing rooms or spaces where light may not reach different surfaces or areas depending on the lamp position. You may want to position the lamp at one side of the room, and change it to the opposite side during a second session. If the lamp is placed in the center of a room, you may also want to place the lamp higher or lower during different sessions in order to guarantee UVC light can reach under furniture as well.

If a UVC lamp is used in a toilet, you can take full advantage of mirrors as they will help bounce light around and expand the reach of UVC light. On the other hand, shower glasses will completely block the light, forcing you to place your portable UVC lamp inside the shower as well. Remember: glass blocks 100% of UVC light. Anything that is located behind a glass will not be affected by UVC light, even if they become illuminated by the light source.

Boxes and Cases

Without knowing how UVC light works, people tend to use UVC cases in ineffective ways. The most common (wrong) way is to completely fill the case with objects or putting objects that are too large to fit inside of it. Filling the case with as many objects as possible when you sanitize them will drastically prevent light from propagating and bouncing around. For example, if you use a UVC case to sanitize fruits or soda cans, try to put just one or two each time. This will allow the directional LEDs inside the case to fully reach all sides of the objects being sterilized.

It's very tempting to squeeze large stuffed toys or pillows inside UVC cases like you're using a laundry machine, but the lack of empty space for light to propagate will result in precarious sanitization (if not none at all).

Portable Wands

UVC wands are different from lamps and cases because you decide where to point them and for how long. In this scenario, speed is key. Fast movements are not recommended as UVC light needs time to sanitize things. The best way to use a wand is by doing very slow and gentle movements around objects or across surfaces. Rule of thumb: the slower the better.

Extra care must be taken when using wands. Even though most products have security locks and sensors that stop the light when the wand is turned up, it's highly recommended that you use glasses and gloves while operating a wand. Shiny or metallic objects may reflect UVC light back to your face and skin, which is something you may want to avoid as much as possible.

The impact of ultraviolet radiation on human health has implications for the risks and benefits of sun exposure and is also implicated in issues such as fluorescent lamps and health. Getting too much sun exposure can be harmful, but in moderation, sun exposure is beneficial.

Beneficial effects

UV light (specifically, UVB) causes the body to produce vitamin D, which is essential for life. Humans need some UV radiation to maintain adequate vitamin D levels. According to the World Health Organization.

There is no doubt that a little sunlight is good for you. But 5 to 15 minutes of casual sun exposure of hands, face and arms two to three times a week during the summer months is sufficient to keep your vitamin D levels high. Vitamin D can also be obtained from food and supplementation. Excess sun exposure produces harmful effects, however.

Vitamin D promotes the creation of serotonin. The production of serotonin is in direct proportion to the degree of bright sunlight the body receives. Serotonin is thought to provide sensations of happiness, well being and serenity to human beings.

Skin conditions

UV rays also treat certain skin conditions. Modern phototherapy has been used to successfully treat psoriasis, eczema, jaundice, vitiligo, atopic dermatitis, and localized scleroderma. Furthermore, UV light, in particular UVB radiation, has been shown to induce cell cycle arrest in keratinocytes, the most common type of skin cell. As such, sunlight therapy can be a candidate for treatment of conditions such as psoriasis and exfoliative cheilitis, conditions in which skin cells divide more rapidly than usual or necessary.

Harmful effects

In humans, excessive exposure to UV radiation can result in acute and chronic harmful effects on the eye's dioptric system and retina. The risk is elevated at high altitudes and people living in high latitude areas where snow covers the ground right into early summer and sun positions even at zenith are low, are particularly at risk. Skin, the circadian system, and the immune system can also be affected.

Ultraviolet photons harm the DNA molecules of living organisms in different ways. In one common damage event, adjacent thymine bases bond with each other, instead of across the "ladder". This "thymine dimer" makes a bulge, and the distorted DNA molecule does not function properly.

Sunburn effect (as measured by the UV index) is the product of the sunlight spectrum (radiation intensity) and the erythemal action spectrum (skin sensitivity) across the range of UV wavelengths. Sunburn production per milliwatt of radiation intensity is increased by nearly a factor of 100 between the near UVB wavelengths of 315 and 295 nm.

Skin damage

Overexposure to UVB radiation not only can cause sunburn but also some forms of skin cancer. However, the degree of redness and eye irritation (which are largely not caused by UVA) do not predict the long-term effects of UV, although they do mirror the direct damage of DNA by ultraviolet.

All bands of UV radiation damage collagen fibers and accelerate aging of the skin. Both UVA and UVB destroy vitamin A in skin, which may cause further damage. UVB radiation can cause direct DNA damage. This cancer connection is one reason for concern about ozone depletion and the ozone hole.

Eye damage

Signs are often used to warn of the hazard of strong UV sources.

The eye is most sensitive to damage by UV in the lower UVC band at 265–275 nm. Radiation of this wavelength is almost absent from sunlight but is found in welder's arc lights and other artificial sources. Exposure to these can cause "welder's flash" or "arc eye" (photokeratitis) and can lead to cataracts, pterygium and pinguecula formation. To a lesser extent, UVB in sunlight from 310 to 280 nm also causes photokeratitis ("snow blindness"), and the cornea, the lens, and the retina can be damaged.

Protective eyewear is beneficial to those exposed to ultraviolet radiation. Since light can reach the eyes from the sides, full-coverage eye protection is usually warranted if there is an increased risk of exposure, as in high-altitude mountaineering. Mountaineers are exposed to higher-than-ordinary levels of UV radiation, both because there is less atmospheric filtering and because of reflection from snow and ice. Ordinary, untreated eyeglasses give some protection. Most plastic lenses give more protection than glass lenses, because, as noted above, glass is transparent to UVA and the common acrylic plastic used for lenses is less so. Some plastic lens materials, such as polycarbonate, inherently block most UV.