TheiaUV’s next generation 222nm UV technology finally breaks down the barriers for mass adaptation.

Not All Ultraviolet Lights Are Created Equal

Ultraviolet light is electromagnetic radiation with a wavelength shorter than visible light but longer than x-rays.  UV spectrum is commonly divided into three distinct bands. UV light with wavelength between 315 and 400 nanometers is called UV-A. UV-A is what gives you the sunburn. UV-B’s wavelength is between 280-315 nm.  It can cause more damage to living cells, but thankfully, UV-B is largely absorbed by the ozone layer high in the atmosphere. The UV band most used for disinfection is the UV-C band with wavelength between 100 and 280 nm. This is because the energy carried by photon increase as the wavelength shortens. UV-C is almost completely absorbed by the atmosphere. In fact, ozone is 100 time more efficient at absorbing the UV radiation at 250 nm than it is at 350 nm.

A Brief History of UV Disinfection

The effect of UV-C disinfection was first discovered in 1877 by British Physiologist Arthur Downes and scientist Thomas P. Blunt when they realized that sunlight can kill and inhibit the development of bacteria in test tubes. 25 years later, the German Ophthalmologist Ernst Hertel discovered that it is the light in the UV-C wavelength, rather than UV-A or UV-B that is the most effective at killing microorganisms.

Later, in the 1930s and 1940s, a Harvard engineer named Willam F. Wells discovered that bacteria and viruses can be transmitted to human through air.  He demonstrated that upper room UV-C irradiation can prevent measles spread in public schools.

Among the many types of UV-C lamps available on the market, the 254 nm UV lamp is the most commonly available and cost-effective type. It is also devastatingly effective in damaging genetic materials found in its path. The 254 nm UV light was invented in 1901 in the form of low-pressure mercury-vapor lamp.  Despite over a century of incredible success as a germicidal weapon, it was only recently science finally revealed the secret behind its power. In DNA’s four-letter alphabet of nucleotides, thymine (T) and cytosine (C) are particularly susceptible to UV. The UV knocks an electron loose and causes two T molecules or two C molecules to bond together, introducing an error into a string of DNA. With sufficient damage to the DNA, the microorganism loses its ability to reproduce. As luck has it, the 254 nm wavelength is also very close to the peak of the DNA absorption spectrum, further enhancing its potency.

Recent advances in semiconductor engineering made available LEDs in the UV-C band.  UV-C LEDs has the potential of very high efficiency, greater durability, and wide spectrum.  However, still in its infancy, UV-C LED has a long way to go before matching or exceeding the efficiency and output level set forth by the mercury-vapor lamps.

Excimer UV lamp was discovered independently in 1913 by Curtis in Britain and Goldstein in Germany.  The acronym excimer stands for excited dimer, meaning an excited state of a two-part molecule.  Excimer lamps based on dielectric-barrier discharge (DBD) principle received a lot of interest since 1980s due to several distinct advantages of the DBD lamps. DBD lamps can be made to emit at specific peak wavelength ranging from 126nm to 354nm.  They can be made to produce very high intensity output, sometimes in the kW/cm^2 range.

The KrCl DBD lamp with 222-nm peak wavelength has been specially interesting.  It resides in the goldilocks zone of the UV spectrum.  222-nm UV light exhibited exceptional germicidal efficiency due to its shorter wavelength and higher photon energy.  Its short wavelength cannot penetrate the outer dead-cell layer of human skin, making it significantly safer in comparison to the 254-nm wavelength.  222-nm wavelength is also sufficiently long that it does not produce ozone.  Shorter wavelength UV such as 172-nm wavelength produces significantly amount of ozone which is harmful to human.

Pulsed-UV is another solution that are available from a few manufactures. Pulsed-UV is broad spectrum and high intensity.  As the name suggests, the UV lights are produced in low-frequency pulses.  Pulsed-UV can be an effective source for decontamination on an on-demand basis.  Due to the service life limitation, it is not suitable for long term continuous operation, nor can it be used in occupied space.

Comparison of 222-nm & 254-nm UV Technology

254-nm UV Technology

Pros:

  • Low-pressure mercury lamp has a highly concentrated output at 253.7 nm wavelength, which is close to the DNA absorption peak at 260 nm.
  • As such, mercury lamps are highly effective in killing pathogens.
  • Mercury lamp technology is very mature and cost effective.

Cons:

  • Not safe for human exposure; can cause skin cancer or cataracts.
  • Takes minutes under normal conditions to achieve 99% or higher kill rate.
  • Some pathogens have developed the ability to repair DNA damage caused by this wavelength UV.
  • Contains mercury.

Both 222 and 254 nm UV lights can cause DNA lesions. These lesions distort DNS’s structure, thereby impeding transcription and replication.

222-nm UV Technology

Pros:

  • Significantly safer to human; 222 nm wavelength is blocked by the top layer of skin (stratum corneum).
  • Exhibits higher germicidal efficacy by damaging DNA/RNA as well as proteins, enzymes, lipids (cell membrane), etc.
  • Does not contain mercury- a dangerous heavy metal.
  • Instant on (no warm-up time required) and long lifespan.
  • Not affected by temperature or humidity.

Cons:

  • Many manufacturing challenges had made lamps at this wavelength scarce – only available in small scale manual production.
  • Traditionally very expensive.

222nm UVC wavelength could not penetrate the outer dead skin or the corneal epithelium of the eye

Why isn’t 222nm UV more widely used?  What has Theia done to change that?

222-nm UV is relatively new to the market.  Challenges in designing, engineering, and manufacturing made it extremely difficult to mass produce and bring the 222-nm UV products to market. The limited 222-nm products on the market have been cost-prohibitive as a result. The key to bring the benefit of 222-nm technology to the world, is to overcome the affordability barrier.

With a group of world-class experts from multiple engineering and years of hard work, Theia has overcome these challenges and is now offering customers 222-nm products with ultra-high output, high efficiency, long lifespan, and reliable operation, at significantly reduced cost.  With optional fully managed service, we can further reduce the upfront capital expenditure for our clients.