Information on the Effects of UV Light & Bacteria Growth

Although ultraviolet (UV) light from the sun plays a significant role in our environment and positively affects nearly everything living, negative consequences of overexposure have been well documented in scientific literature. Skin cancer, cataracts, premature skin aging and immune system suppression all have been linked to excessive amounts of UV energy. UV light does its damage at the cellular level, and its devastation can affect organisms as complicated as human beings or as simple as bacteria.

Types of Light

• The sun emits three types of light: visible light that is seen, infrared light that is felt as heat and invisible UV light (radiation). UV light exists as three types, as well. UV-A energy deeply penetrates skin and is the type of UV light required for the body's production of vitamin D. UV-B penetrates less deeply and is responsible for skin burning. UV-C energy is the most damaging of the UV light types. Fortunately, it is absorbed by the atmosphere before reaching Earth.

UV-C and Bacteria

• UV-C is the type of UV light that eliminates the growth of bacteria. In fact, UV-C is not only bactericidal, it is germicidal and effectively eliminates viruses, parasites and fungi in addition to bacteria. UV-C destroys pathogens (disease-causing organisms) by deactivating their DNA and RNA. As a result of having their genetic material altered, the microorganisms are unable to reproduce and cause disease. Germicidal lamps are used by scientists for the production and emission of antimicrobial UV-C energy.

Dosage

• The dosage of UV-C is measured in microWatt-seconds per square centimeter. In other words, dose depends upon the power of the light source (microWatts), the amount of time of the exposure (seconds) and the size of the area exposed (square centimeters). The dose of UV-C required to kill microorganisms effectively varies by type of pathogen. For instance, a dose of 2,760 microWatt-seconds per square centimeter kills the bacteria responsible for Legionairre's disease, yet a dose of 10,000 microWatt-seconds per square centimeter is required to kill the bacteria that cause tuberculosis.

Applications

• UV light has numerous applications as a means of eradicating bacterial growth. Initially, its use was limited to hospitals and industrial facilities that required sterile equipment and sterile working environments. Today, it serves to sterilize air, water and surfaces in a variety of settings, including the home. Producers of hand-held UV light devices claim the products kill 99 percent of bacteria such as salmonella and staphlycocci within one minute of exposure.

Limitations

• Although UV light is a highly effective agent against bacterial growth, it has limitations. UV-C energy is not very penetrating, and the radiation must reach microorganisms in order to kill them. Consequently, the light must be kept clean, and the bacteria must be in an environment that is transparent. Contaminants such as dust and debris in air or water interfere with disinfection. Also, UV light intensity diminishes over time and, therefore, requires regular monitoring. The special safety precautions that must be taken when utilizing UV light as a method of sterilization are also a limiting factor.