What is UVC light? How is it different from UVA and UVB light?
UVA, UVB, and UVC light are all naturally emitted by the Sun. Long wave length UVA light is relatively harmless and is able to penetrate the Earth's atmosphere to its surface. Medium wave length UVB light is, for the most part, absorbed by the ozone; although a percentage of UVB light does reach the surface. Short wave length UVC light is quickly absorbed by the air; a very negligible amount ever reaches the Earth's surface.
UVC light has the shortest wavelength at 280 nm to 100 nm, and is therefore the highest in energy. When this high energy light hits living organisms, the damage done is severe.
How does UVC light sterilize?
DNA strands are made up of bases - adenine, thymine, guanine, and cytosine - that bond in pairs, creating a double helix. As high energy UVC light bombards a cell, the bonds between these base pairs are broken and new bonds form between bases on the same side of the DNA strand, creating 'bridges.' These bridges disrupt the DNA's double helical structure, rendering it incapable of coding for basic cellular functions, including reproduction. The DNA is corrupted and the organism is no longer able to survive.
This is what is happening in HVAC systems equipped with UVC air purifiers. The UVC light is destroying bacteria, viruses, and molds. Studies done have found whole-house UVC air purifiers to be up to 75% effective at inactivating fungal spores (molds) and a whopping 97% effective at inactivating bacteria in the home!
1. Kujundzic, E, F Matalkah, CJ Howard, M Hernandez, and SL Miller. "IV air cleaners and upper-room air ultraviolet germicidal irradiation for controlling airborne bacteria and fungal spores." J Occup Environ Hyg. 3.10 (2006): 536-46. Print.
2. Sinha, Rajeshwar P., and Donat P. Häder. "UV-induced DNA damage and repair: a review." Photochemical & Photobiological Sciences. 1 (2002): 225-236. Print.
3. Wikipedia contributors. "Ultraviolet." Wikipedia, The Free Encyclopedia.