Understanding how ultraviolet light works is easily understood when you dissect the science behind it. We’ll walk you through an easy-to-understand physics course to explain how light can kill microorganisms.
Let’s explore how ultraviolet light works, why it is an effective tool for killing harmful germs in the environment, and why wavelengths play an important role in disinfection time.
What is ultraviolet light and how does it kill microorganisms?
Ultraviolet light is a form of light made naturally by the sun. It is divided into three sections, UV-A, UV-B, and UV-C. Those sections describe a range of wavelengths, or the unit we use to measure light (see image). These wavelengths are measured in nanometers (nm), which is a billionth of a meter. Our eyes cannot detect wavelengths this small, so UV light is invisible to us.
UV-A and UV-B are commonly recognized for their ability to cause skin damage in high doses, and UV-A is often known as “black light”. UV-C isn’t as well known, because the ozone layer around the earth absorbs it and it doesn’t reach us on the ground.
UV light is a form of energy. Some of those forms of energy are able to cause atom-level damage. UV-C is able to cause this type of damage to germs because it’s got just enough of the right energy to penetrate the cell walls and damage DNA.
Key points about UV-C: it’s invisible, it’s energy, it isn’t naturally found on earth, and it has a range of wavelengths.
How does UV-C kill microorganisms?
At the most simplified level, UV-C kills microorganisms because the structures of the microorganism absorb that energy and experience damage. However, it gets a lot more complicated when you ask the right questions:
Do all wavelengths of germicidal UV cause equal damage to a germ?
No. Within the range of 200-315 nm, research has shown the sweet spot may be between 200 and 240 nanometers1. That means the 200-240 nm range is 9 times more lethal than most other areas of the UVC range.
This graph shows us that a bacteria that is a surrogate for C.difficile, as well as two different viruses, were more sensitive to UVC in the range of 200 to 240.
Do all germs get killed by UV-C?
That depends on the wavelength of UV-C that’s being used, and the intensity of it. Bacteria that form spores, some fungi, and certain viruses are pretty tough to kill if you aren’t producing light in the 200-240nm sweet spot range described above. If the germs are exposed to other wavelengths at a certain intensity for a longer time period, they will usually eventually die. That combo of intensity and time is what some people call “dosage”.
Do all parts of the germs experience the same damage?
They do not, and here’s why. Different wavelengths cause different types of damage. For example, 220 to 240nm cause damage to proteins in the cell wall – pretty useful when busting open a spore or damaging a fungal cell’s thick walls – while DNA damage is highest at 265nm. Why? The damages being done are to different types of molecules, which absorb wavelengths in varying ways. So the bonds in DNA are most sensitive to 265nm.
Key points about UV and germs: Different wavelengths have different effectiveness in killing pathogens. Germs are not all killed at the same rate, and spore-formers are tougher to kill.
The Most common types of UV Disinfection:
You’ll see two main types of UV products being used for room/area disinfection. One typically has multiple long bulbs that surround the product (frequently referred to as a tower) These bulbs are Low Pressure Mercury bulbs that emit UV-C consistently at 254nm. Peer reviewed research shows sporicidal disinfection times can be between 45-52 minutes for these products.2 The other is a single lamp that raises and lowers, putting out pulses of UV light. This is a Pulsed Xenon lamp. It emits high-intensity, full spectrum UV light (200-315nm). The intensity and broad spectrum nature are known for quickly and effectively deactivating pathogens where they are most susceptible. Research conducted on sporicidal cycle times for the Pulsed Xenon lamp is 5 minutes, a fraction of the time3.
LightStrike™ Robots from Xenex® utilize Pulsed Xenon to create UV light that quickly and effectively deactivates harmful pathogens on surfaces where pathogen transmission to patients is most likely to occur. This proven, evidence-based solution has been adopted by over 900 facilities worldwide for it’s disinfection speed, ease of use and ability to deactivate pathogens to help reduce the likelihood of pathogen transmission.
Beck et al. Water research, ISSN: 1879-2448, Vol: 70, p27-37
Anderson DJ, et al. ICHE. 2018;39(2):157-63.