How Does UV Light Kill Germs?

Ultraviolet Basics

With all of the dubious gadgets and sprays marketed to neat freaks and germophobes, it is hard to believe that shining light on something would kill germs. Nonetheless, the right kind of ultraviolet light is actually an extremely effective germicide, able to kill more than 99 percent of germs. Ultraviolet lamps are used in sewage treatment plants, hospital clean rooms and many other areas where killing bacteria, viruses and spores is crucial. Combined with good housekeeping and duct maintenance, an ultraviolet system can help to ensure that your household air supply is as sanitary as possible.

The Right Light

Ultraviolet light is a type of high-frequency light above the visible spectrum. Different wavelengths of light are absorbed by different materials, and the same goes with ultraviolet. Ultraviolet cleaners use light at a particular wavelength---254 nanometers. This frequency of light is emitted by the sun and other stars, but most of it is absorbed by the atmosphere, so it is very rare on the surface of the earth. Specially made ultraviolet lamps, however, can produce a great deal of it.

How It Works

The particular wavelength of light used is absorbed by DNA. The light causes mutations in the DNA. Since the DNA encodes what proteins organisms make, organisms damaged by UV light are unable to continue to make the proteins which keep them alive and allow them to reproduce. Bacterias and fungii are single-celled organisms, so they have nothing but a thin cell membrane separating them from the ultraviolet, and the waves pass easily through. Viruses are even more vulnerable, since they don't have cell membranes. The ultraviolet light will not necessarily kill the bugs outright, but it will weaken them and render them unable to cause harm or survive for long.

Limits of UV Light

Ultraviolet light is only able to harm bugs that it contacts. Even a small crack can hide spores in its shadow, keeping them safe from the UV. High-intensity ultraviolet lights are also harmful to people, so you can't use UV in your living space. Ultraviolet cleaning systems won't necessarily do anything for allergies, since even a dead or damaged spore of fungus can aggravate the immune system, causing an allergic reaction. Finally, UV light can't do anything about contaminants introduced downstream from it. If you have a UV air cleaner with leaky ducts, contaminants can seep in, polluting your household air after the UV light has sanitized it.