What is UVC?

How does UVC disinfection work?

Research studies and reports has shown that DNA, RNA, and proteins in biological organisms absorbs UVC light energy in the range of 200 nm to 300 nm.

When proteins absorp UVC light energy, it can lead to rupture of cell walls and death of the organism. Similarly, absorption by DNA or RNA (specifically by thymine bases) is known to cause inactivation of the DNA or RNA through the formation of thymine dimers. When enough of these dimers are created in DNA, the DNA replication process is disrupted, and the cell cannot replicate.

Comprehensive studies have shown different levels of UVC energy is required to invalidate different micro-organisms including Covid-19 or SARS-CoV-2 (Reference: FDA) .  Examples as shown:
Ultraviolet (UV) light, or beyond violet, is the invisible component of the electromagnetic spectrum that falls in the region between visible light and X-Rays.

UV radiation includes light of wavelength range of 10 to 400nm. The UV light is subdivided and categorized into four separate regions:

10 nm to 200 nm      

200 nm to 280 nm   

280 nm to 315 nm    

315 nm to 400 nm    

No measurable UVC from the sun reaches the earth’s surface.  As such UVC lights are created to harness its useful disinfection properties.

Why it is essential to measure UV-C energy!

If UV-C light eliminates micro-organism simply with exposure, why does it matter if we measure the UV-C energy received at the surface?  Why don't we simply use the highest power lamp available and then leave it on for as long as we need?

The simple answer is :
            In use, the effect may not be what the lamp was designed for and result may not be what the user has intended.

In fact, it is essential to measure the UV-C energy directed on the surfaces of interest each time disinfection takes place, not periodically or every other disinfection.

The detail reasons are as follows:
            1. UV-C energy, not irradiance, inactivates micro-organism  
            2. UV-C is invisible
            3. UV-C lamp power may change over time
            4. UV-C irradiance weakens over distance
            5. UV-C irradiance is easily blocked
            6. UV-C degrades materials and is harmful to living organisms including human

1. UV-C energy, not irradiance, inactivates micro-organism

UV-C’s germicidal or germ killing effects are well proven. The UV-C wavelength owes these destructive effects to the biocidal features of ionizing radiation.

The ionization process drives UV-C’s power to alter chemical bonds. The 254 nm wavelength carries enough energy to excite doubly-bonded molecules into a permanent chemical rearrangement, causing lasting damage to DNA, ultimately killing the cell. Even a very brief exposure to UV-C can permanently eliminate microbial replication. In other words, UV-C exposure kills bacteria and other infection-causing microbial (and efficiency-robbing) organic contaminants. After being killed, organic remnants are subject to disintegration.  (Reference : uvresources.com)

Hence the requirement for a very powerful UV-C lamp is not critical.  Lower powered lamp is still good as it only requires longer exposure till the desired energy level is reached.   While high-powered lamp can reduce the amount of time required for each disinfection, generally, high-power lamps are more expensive; requires more power thus making it not battery friendly; too heavy or consumes too much power for robotic deployment.

2. UV-C is invisible

While almost all UV-C lamps irradiates purplish or bluish lights which is often associated with UV-C light, the reality is UV-C component is invisible to most humans.  The near violet or near blue rays are just nearby bands of visible light release when UV-C is generated.  So the purplish or bluish ray do not necessary indicate presence of UV-C light.  The only way to ascertain UV-C presence is to actually measure the presence.  (Reference : Wikipedia)

3. UV-C lamp power may change over time

As with all electronics, UV-C lamp degradates over use.  While regular maintenance and recalibrations is essential and can keep the lamps performance in check, there is no guarantee that it will perform to specification when used.  As such rather than assuming it is suppose to perform to specification, it is essential to know exactly the energy level delivered to the target surfaces everytime the lamp is used.

4. UV-C irradiance is affected by distance

While the power and output of a UV-C lamp are important, the distance of the UV lamp to the surface of interest is just as important. 

Distance is of particular interest due to the inverse-square-law of emitted light and UVC rays - for every 2x increase in distance, irradiance decreases 4x fold as shown here:

5. UV-C irradiance is easily blocked

Studies has shown that UV-C energy cannot pass through clear acrylic, clear plastics, metal and many other materials.  Even naturally ocurring UVC from the sun is blocked by ozone layer in the atmosphere. (Reference : FDA)

As such, there is no certainty a surface of interest is properly disinfected unless a sensor, placed strategically, is used.

6. UV-C degrades materials and is harmful to living organisms including human

UVC lamps used for disinfection purposes may pose potential health and safety risks depending on the UVC wavelength, dose, and duration of radiation exposure.

Direct exposure of skin and eyes to UVC radiation from some UVC lamps may cause painful eye injury and burn-like skin reactions. Never look directly at a UVC lamp source, even briefly.

UVC can degrade certain materials, such as plastic, polymers, and dyed textile. (Reference: FDA)

Hence, usage of UV-C lamps should be kept to the minimum.  Extended exposure beyond the required dosage do not bring value but increases the possibility of harmful effect.
Copyright Fidelity Technologies Pte Ltd October 2021
Far UV or vacuum UV

UVC - useful for disinfection and sensing

UVB - useful for curing, and medical

UVA (or “near UV”) - useful for printing,
curing, lithography, sensing and medical