Ultraviolet light (UV) is a type of naturally present electromagnetic radiation that is in sunlight and actually makes up approximately 10% of the total light generated by the sun. UV light is electromagnetic energy with wavelengths shorter than visible light but longer than x-rays (see image below).
The wavelength of this light ranges from 10nm to 400nm and is classified into three sub-bands; UV-A (near), UV-B (middle), and UV-C (far).
UV light with wavelengths less than 290nm are considered to have “germicidal” properties (more on this below). Earth’s atmosphere absorbs ultramagnetic radiation with wavelengths less than 290nm, meaning that most of the UV-C and UV-B generated by the sun is blocked by our planet’s ozone.
Learn about all of the applications for UV light here.
The disinfection properties of ultraviolet lighting have been known for over 140 years, since Downes and Blunt discovered the antibacterial effects of the shorter wavelengths of sunlight. Shortly thereafter, it was proven that the UV portions of the light spectrum were able to destroy microorganisms.
After confirming UV lighting’s ability to kill pathogens, the next step was to find a way to replicate the UV wavelengths that would result in the disinfection of surfaces, air, and water. The first UV quartz lamp was invented in 1904 and resulted in the germicidal lamp. Germicidal lamps are a type of lamp that produce the wavelengths of ultraviolet light (UV-C; 200nm to 280nm) that have disinfection properties, like the ones used in this study to reuse N95 masks during the coronavirus pandemic.
Vintage UV Quartz Lamp
As mentioned, UV light with wavelengths less than 290nm are considered to have “germicidal” properties, meaning it can kill germs. This kind of light is commonly used to kill microbes on surfaces, in air, and in water.
Ultraviolet light kills cells by damaging their DNA. Exposure to the electromagnetic radiation (light) at certain UV wavelengths modifies the genetic material of microorganisms and destroys their ability to reproduce. The UV energy triggers the formation of specific thymine or cystosine dimers in DNA and uracil dimers in RNA, which causes the inactivation of microbes by causing mutations and/or cell death as well as failure to reproduce. (source)
According to this article from the Centers for Disease Control (CDC), “UV can kill all bacteria, including drug-resistant bacteria because UV light is actually attacking the DNA and RNA of microbes. While the amount of UV needed to kill a microbe may vary as there is a relationship between the size of DNA molecules and the effect of UV radiation, there have been no reports of microbes demonstrating an ability to build an immunity to light-based methods.”
We have an entire blog post specifically about UVGI here.
In summary, UVGI is a method of disinfection that uses short wavelength ultraviolet light (UV-C) to inactivate or kill microorganisms and pathogens. Essentially, UVGI decontamination is the use of UV light with sufficiently short wavelengths to disinfect surfaces, air, and water.
UVGI has been recommended or used for the isolation of disease and bio-defense systems for buildings by the United States Army, the CDC, and the Federal Emergency Management Agency (FEMA).
The effectiveness of germicidal UV light depends on the length of time a microorganism is exposed to UV, as well as the intensity and wavelength of the UV radiation.
It is important to understand the difference between sterilization, disinfection, and decontamination as these terms are often incorrectly used interchangeably, which can cause confusion in regards to the effectiveness of UVGI (as well as the avoidance of potential legal ramifications).
Sterilization
Per the CDC, sterilization describes a process that destroys or eliminates all forms of microbial life and is carried out by physical or chemical methods.
Disinfection
Per the CDC, disinfection describes a process that eliminates many or all pathogenic microorganisms on inanimate objects.
Decontamination
To decontaminate is to make an object or area safe by removing, neutralizing, or destroying any harmful substance.
Basically, decontamination is the result after the processes of sterilization or disinfection.
Per the CDC, disinfection and sterilization are essential for ensuring that medical and surgical instruments do not transmit infectious pathogens to patients. Because sterilization of all patient care items is not necessary, healthcare policies must identify, primarily on the basis of the items’ intended use, whether cleaning, disinfection, or sterilization is indicated.
Yes! Let’s take each individually below.
Air—UV lighting can disinfect the air in several ways. Commonly, UV-C lamps are used in ceiling fixtures or HVAC systems to clean circulating air continuously. The lamp itself has a shield so that the radiation is only directed upwards as to not harm people (more on safety and UV lighting here). Also, they’re far enough away from the ground that people are not hurt by the distant radiation and they cannot be touched.
Surfaces—This is like using UV lighting to kill pathogens on materials, objects, and surfaces, as well as PPE and other healthcare equipment. No one is in the room while UV disinfection lighting units are operating. Like in this Duke University study, which proves UV lighting can kill pathogens even in hard to reach corners and drawers of a hospital room.
Water—UV lighting is a common way to kill pathogens in water, especially in municipalities. Municipalities use the technology in their water treatment plants and on waste water. People even use UV lighting in their homes’ piping. It’s simple—a UV lighting unit is placed in the water to disinfect.
There are two basic types of commercially viable lamps that provide the UV-C necessary to be germicidal. We define commercially viable as systems or lamps that provide the necessary UV-C light intensities and dosages that are actually able to disinfect larger areas and surfaces. There are other light sources of UV-C, such as LED, that do provide ultraviolet light in the necessary germicidal wavelengths of 100nm to 280nm, but they are not currently able to provide the intensity of light needed to disinfect surfaces.
Most of these lamps are sold as components in a complete disinfection system, or as linear/compact lamps. The types are:
Lower pressure mercury lamps
These lamps are very similar to conventional fluorescent lamps in shape and form, however, the UV-C lamps lack fluorescent phosphor and are often made of fused quartz, as opposed to borosilicate glass. This allows the light produced by the mercury arc within the lamp to pass out of the glass unmodified, generating light in the germicidal ultraviolet wavelength.
Pulsed xenon
Xenon arc lamps are a type of gas discharge lamp that generates light by passing electricity through ionized xenon gas.
Often use flashes lasting a few milliseconds of germicidal ultraviolet light every six seconds or so
Pulsed UV light systems such as pulsed xenon are able to combine the germicidal effects of UV-C lighting with the thermal disintegration of cell walls from the intensity and speed of the photonic delivery.
Low pressure mercury vs. pulsed xenon
Although low pressure mercury (LPM) lamps provide germicidal UV-C light, unless they are higher wattage lamps (100 watts or more) they will have a hard time effectively disinfecting surfaces from further distances.
They also lose efficacy (lumens per watt) quickly, needing to be replaced every six months if used frequently.
LPM lamps produce UV-C at the 253.7nm wavelength, which, while an effective wavelength range for germicidal purposes, there are some adverse effects in regards to duration required for disinfection across a broader range of bacteria and viruses.
LPM lamps also provide a “constant” dose of UV-C lighting, meaning they are on at full power for the duration of a disinfection cycle. This can result in higher levels of damage to plastics and other materials than other sources of UV disinfection lighting.
Pulsed xenon lamps generate light in a much smaller form factor, and as a result are able to direct UV light with more precision without losing intensity. This means they can be placed further away from objects and materials and cover larger areas without losing effectiveness.
Pulsed xenon lamps also do not lose efficacy nearly as fast, often lasting up to 2.5 million pulses, depending on the manufacturer of the lamp.
In addition, pulsed xenon lamps generate a wider wavelength range of germicidal UV light (200nm – 315nm). This range of UV light has additional germicidal properties; for example, UV-C light at 222nm has been shown to reduce spore forming bacteria faster than the 253.7nm wavelength produced by lower pressure mercury lamps.
In regards to potential damage to surfaces or materials, since pulsed xenon do not use “constant” UV-C light to disinfect, pulsed xenon has been shown, over a 12 year study, to result in NO degradation to materials in hospital settings.
A good way to compare the two UV-C lights sources...
Imagine that low pressure mercury lamps are like a garden hose, whereas pulsed xenon is like a power washer. The power washer uses less water, but forces that water out at a much higher PSI. Lamps that use a pulse compared to a constant stream produce more intense light. The capacitors in pulsed xenon lamps store their electrical charges and then release UV-C light in millisecond pulses. Pulsed xenon light releases more powerful photons than LPM lamps, rendering pathogens unable to reproduce or repair themselves, resulting in faster disinfection results.