UV Light for Disinfection
UV has been used for disinfection since the mid-20th century, with beginnings even earlier when sunlight was investigated for bactericidal effects in the mid-19th century. It’s used for drinking and wastewater treatment, air disinfection, the treatment of fruit and vegetable juices, as well as a myriad of home devices for disinfecting everything from toothbrushes to tablet computers. Within research facilities, UV has been an option when purchasing biological safety cabinets for years, and can also be used within ductwork.
UV technology has advanced in recent years to become more reliable. Ballasts being used today are able to maintain the power output of UV bulbs for far longer than in the past. UV bulbs today have rated lifespans in the thousands-of-hours. This has allowed UV systems to become more viable for wide ranging use
The use of UV has recently grown within the healthcare industry to provide disinfection of room surfaces in addition to existing cleaning methods. The use of ultraviolet light for surface disinfection within research facilities has started to increase as well due to its ease of use, short dosage times, and broad efficacy.
How Does UV Work?
Ultraviolet light exists within the spectrum of light between 10 and 400 nm. The germicidal range of UV is within the 100-280nm wavelengths, known as UV-C, with the peak wavelength for germicidal activity being 265 nm. This range of UV light is absorbed by the DNA and RNA of microorganisms, which causes changes in the DNA and RNA structure, rendering the microorganisms incapable of replicating. A cell that can’t reproduce is considered dead; since it is unable to multiply to infectious numbers within a host. This is why UV disinfection is sometimes called ultraviolet germicidal irradiation (UVGI).
Lucentᵘᵛ systems use low-pressure, mercury arc germicidal UV lamps which are designed to produce the highest amounts of UV radiation - where 90% of energy is typically generated at 254nm. This radiation is very close to the peak of the germicidal effectiveness curve of 265nm, the most lethal wavelength to microorganisms.
What is UV Effective Against?
UV has been proven effective against a broad spectrum of microorganisms. Viruses contain RNA or DNA and are thus susceptible to irradiation. UV-C light has been shown to swiftly inactivate our world’s most concerning viruses including Coronavirus, Ebola, and Influenza. Bacteria and fungi both contain DNA and are similarly vulnerable to UV light. Spores are also susceptible to UV.
As UV-C provides radiation, it is not safe to be in the room while UV-C disinfection is taking place. UV-C is classified as “reasonably anticipated to be a human carcinogen” by the National Toxicology Program. It presents a hazard to skin and eyes, so direct exposure to UV-C is always to be avoided. UV-C is blocked by a number of materials, including glass (but not quartz glass) and most clear plastics, so it is possible to safely observe a UV-C system if you are looking through a window.
UV-C provides residue free disinfection, so there is no concern over dangerous residues that need to be wiped down or neutralized after the disinfection occurs. The process is environmentally friendly in that there are no dangerous or toxic chemicals that require specialized storage or handling. Since no chemicals are added to the air/water, there are no process byproducts to be concerned with. The UV bulbs do not require special handling or disposal either, making the system a green alternative to chemical disinfectants.
Speed and Efficiency
Disinfection times with UV-C are fast, with a typical disinfection cycle lasting about 15 minutes. This allows for extremely fast turnover times for rooms or other spaces being disinfected. Due to its simplicity, UV-C disinfection is easy to understand. All surfaces within a certain distance will observe an assured level of disinfection in a certain amount of time as long as the light is not blocked from shining on that surface. It becomes very easy to plan the use of a UV-C disinfection system when the parameters and limitations are easily established and understood. There is no need to establish air flow patterns with UV-C as you would with a fogging system. Nor is there a need to isolate rooms from HVAC systems or seal doors. This, along with the lack of chemical mixture, makes the preparation time quick to setup and start a UV-C disinfection cycle.
The cost to run UV systems is very low, as systems are powered by regular wall outlets. With that, a typical UV-C treatment costs under two cents. UV systems also require little maintenance and upkeep due to their simplistic nature. UV bulbs last thousands of hours at their peak output, limiting the need for routine consumable change out and maintenance.
While UV is effective at inactivating a wide range of microorganisms, there are limitations for its use. As it involves light waves, UV operates in a “line-of-sight” fashion, only irradiating surfaces within its sightlines. Surfaces can be blocked from the light if objects are in the way, much like a beach umbrella offering protection from the sun.
These areas that become blocked from the UV light are commonly referred to as shadow areas. Surfaces in these shadow areas do not receive adequate disinfection as UV light does not have the ability to reflect well off surfaces. Shadow areas are typically dealt with by moving the UV light source to a second position to accommodate disinfection of the surfaces blocked from UV disinfection the first time. They may also be dealt with by introducing multiple UV-C lights to a space in a single cycle.
Distance also plays a factor into the efficacy of UV light. The strength of the UV-C light decreases the further away it gets from the light source, following the inverse square law. This means that at twice the distance, the UV-C will have ¼ of its power that was present at the original reference point. This relationship limits how far a single source of UV light is effective before it is too weak to provide adequate disinfection. Most systems deal with this by quantifying their UV-C output at a given distance, and using that distance to generate treatment times. Sensors are available which can measure the UV-C output of the UV systems at any location, such that adequate treatment times can be interpreted for that specific location.
UV light does not penetrate well into organic materials, so for best results UV-C should be used after a standard cleaning of the room to remove any organic materials from surfaces.
UV light can safely be used for a variety of disinfection applications. Systems are available to disinfect rooms and high touch areas, ambulances and other emergency service vehicles, ductwork, tools and equipment inside a disinfection chamber, continuous UV-C pass-through conveyors, and many other applications. It also provides a chemical free method of disinfecting soundproofing materials that are traditionally chemically incompatible.
In addition to healthcare facilities and ambulances, UV-C light applications include offices, retail, elevators, mass transit systems, grocery, livery, waiting rooms and other high touch areas.