What is UVC Light?
Invisible to the human eye, ultraviolet (UV) light occurs at wavelengths 100-400nm. It is divided into three types: UVA, UVB, and UVC. You might recognize UVA and UVB as the reason we wear sunscreen. UVC light exists between 100-280nm, and is particularly effective at disinfection. Our system utilizes 254nm UVC bulbs.
How Does UVC Disinfection Work?
The UVC light inactivates microbes by damaging its structure, preventing their ability to replicate. Since it is a light source, it can only disinfect surfaces and air volumes that are within line of sight of the UVC lamps. Current robotic and non-robotic applications for UVC disinfection include hospitals, water treatment, food processing, and in HVAC installations.
The amount of UVC radiation needed to inactivate a microbe is often referred to as the dosage of UVC. The dosage is the intensity of the UVC light over an area, multiplied by the time it has been exposed, reported in milliJoules/cm2. Typically, we state that a D90 dose is the amount of UVC radiation needed to inactivate 90% of the microbial concentration. Similarly, a D99 dose is the UVC radiation that inactivates 99%. It’s important to note that the total dosage needed is not linear with time: in fact, the D99 dose will take twice as long to deliver as a D90 dose.
Why Use a Robot?
The total dosage an area receives depends not only on the time it is exposed to UVC radiation, but also the distance from the UVC light source. An area that is twice as far from the robot will take four times as long to disinfect. With a stationary light fixture, the time to disinfect a room depends on the furthest area the light needs to reach. However, with a mobile robot, we can deliver targeted dosages in a more time-efficient manner.
How Do You Determine Target Dosage Values?
While UVC is effective at neutralizing a number of pathogens and microorganisms, the particular susceptibility depends on the individual microbe. For our applications, we refer to reference literature to determine our target dosage values.
For COVID-19, we specifically look at disinfection thresholds for both airborne particles and surface fomites. Airborne particles are those that stay suspended in air for up to several hours, while surface fomites are droplets that fall from the air and land on surfaces. The UVC dosages required to neutralize airborne particles  are less than what is required to neutralize surface particles [2-4].
Target D99 dosage for fomites on surfaces: 5 mJ/cm2
Target D99 dosage for aerosolized particles: 2 mJ/cm2
Based on the current scientific literature, we target a total dosage of 5 mJ/cm2, which provides the predicted 99% neutralization of COVID-19 on surfaces, and >99% neutralization of COVID-19 airborne particles.
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