Several home air purifier manufacturers have started including an ultraviolet (UV) lamp in their air purifiers. The reason for a UV lamp is that ultraviolet light in sufficient doses kills certain harmful microorganisms like viruses and bacteria. The people who are most at risk from airborne harmful microorganisms are very old people and very young people. That’s why air purifiers with UV stages are often seen in nursing homes and in child care centers and pediatrician offices.
Ultraviolet light is invisible to the human eye. The wavelength of UV light is shorter than the shortest-wavelength light we can see, which is violet. There are three types of UV light: UVA, the longest wavelength UV light; UVB, which is shorter in wavelength than UVA, and the shortest of all, UVC, which is the range of UV light that kills bacteria and viruses. Any type of UV light can damage the eyes and has been linked with the development of skin cancer, so it is very important to protect your eyes when checking on the UV lamp in an air purifier. Chances are that the light in the air purifier will not be direct enough or strong enough to damage eyes, but it is best to be safe.
The way UV light kills harmful microorganisms is that at it scrambles the organism’s DNA. The two wavelengths of UV light that are the most potent for killing bacteria and viruses are 185 nanometers and 265 nanometers. A UV lamp in an air purifier that claims to kill microorganisms should emit energy in one or both of these wavelengths.
The problem with UV lamps in home air purifiers is that the bulbs will still appear to work, because they light up in a violet color, even though they have stopped emitting light in the proper range to kill microorganisms. One way to avoid this problem is that when you put in a new UV bulb, you can write the date on the bottom of the air purifier, or put it on your calendar. The instruction manual that came with your air purifier will tell you how often to replace the bulbs, and you should write down this date or mark it on your calendar as well.
Even though UV rays are great for killing bacteria and viruses, they are not functional unless there is a filter of some sort (like a high efficiency particulate air, or HEPA filter) that filters air before it reaches the lamps. Without a particulate filtering system, there may be enough particulates to shade the microorganisms from the UV light. In most home air purifiers, the UV stage of the process comes last so that the air flowing through the UV light is as particulate free as possible.