The UVC light spectrum
What Is UVC Lighting?
Most people have heard of ultraviolet (UV) light. It’s the part of the electromagnetic, or light, spectrum that falls between X-Rays and visible light. While it’s not visible to the human eye, light that falls within this range of wavelengths reaches the Earth from the sun every day.
What few people realize is that UV light, which includes wavelengths from 100 nm to 400 nm, can be broken down into four categories. UVC light is radiation that has a wavelength of 200-280 nm. Unlike UVA and UVB light, no measurable amount of it reaches the surface of the planet from the sun.
Where Does UVC Light Come From?
While the sun produces UVC light, no significant amount of it penetrates the Earth’s atmosphere to reach the ground. As a result, scientists have had to find a way to synthesize it. They do so by filling evacuated glass tubes with low-pressure argon gas, then adding a small amount of mercury.
When the argon atoms become energized, it pushes electrons through the mercury vapor, liberating mercury electrons. Since mercury’s spectral line sits right around 253.7 nm, the radiation generated by this activity is always considered UVC light.
What Are the Applications for UVC Light?
Wondering why scientists would go through all that trouble to produce UVC light? The reasoning is simple. UVC light is germicidal, meaning it can kill microorganisms that would otherwise pose a risk to human, animal, or ecosystem health.
The reason UVC light is so effective at neutralizing microorganisms has to do with the spectral sensitivity of their DNA, RNA, and proteins. When DNA and RNA absorb UVC radiation, it disrupts the replication process. When proteins absorb UVC light, it causes the organism’s cell walls to rupture. The combined effect is to stop germs from replicating and, in some cases, kill them outright.
Is UVC Light Dangerous to Humans?
UVC light can do serious damage to tiny bacteria and viruses, but it’s not known to cause permanent damage in humans or large animals. Overexposure can cause skin redness and eye irritation, but these effects are temporary. Researchers have not observed any relationship between UVC light exposure and cancer or cataracts. Those are associated with UVB light.
How Does UVC Disinfection Work?
Scientists quantify disinfection, or the inactivation of microorganisms, as a measure of Log Reduction Value (LRV). LRV refers to the number of microbes eliminated by a disinfection technique relative to the original number of live microbes. In the case of UVC light disinfection, the LRV is dose-dependent.
Researchers have performed numerous biological studies on UVC dose requirements for target microbes. The target LRV for most of them is a 3 log reduction, which means that 99.9% of the organisms are killed or inactivated. To reach that target, UVC disinfectant lighting manufacturers tailor strength to different applications.
How Can Users Tell It’s Working?
The most accurate way to tell if UVC light is disinfecting surfaces, water, or air effectively is to sample the affected substrate before and after disinfection. There are, however, also a few signs that people can look for to verify for themselves that UVC disinfection is working. Depending on the application, they may notice:
A reduction in visible mold
Cleaner-looking drain pans or surfaces
Improved indoor air quality (IAQ)
Increased airflow in HVAC systems
What Are the Most Common Applications for UVC Disinfection?
UVC lights can be used to disinfect the air, water, and surfaces in a wide variety of settings, from industrial plants to individual homes. They’re most commonly installed in HVAC systems, where microbial infestations are surprisingly common. However, UVC disinfection can be helpful in any setting where a combination of moisture and darkness would otherwise create a beneficial environment for mold, bacteria, and other microorganisms.
To maximize effectiveness, technicians place the UVC light fixture between 6″ and 50″ from the affected surface. At this distance, the UVC light will be able to degrade all kinds of surface and waterborne contaminants. Cleaning the affected surfaces first increases the speed at which UVC disinfection works.
How Often Do UVC Lamps Need to Be Changed?
UVC lamps must be changed when their output reaches around 80% of its original intensity. Most of the time, that means waiting roughly 12-15 months between bulb changes. Trained technicians can also use radiometers to evaluate UVC lamps’ light intensity. Checking the light intensity annually and changing out the bulbs more frequently is the recommended approach for all infectious disease applications.
UVC light is a powerful tool for disinfecting surfaces and removing air and waterborne organic contaminants. It’s safe, produces no harmful byproducts, and has been proven by extensive research to neutralize up to 99.9% of microbes.