ELF (extremely low frequency)

ELF (extremely low frequency) refers to an electromagnetic field having a frequency much lower than the frequencies of signals typically used in communications. The most common ELF field is radiated by utility power lines. In the United States, this frequency is 60 Hz. You are exposed to these fields whenever you are near electrical appliances of any kind.

In recent years, ELF fields have become a subject of concern in computing applications where cathode-ray tube (CRT) displays are used. These displays, typically used in desktop computer workstations and television sets, generate electromagnetic fields because of the strong, fluctuating currents in the electron-beam deflecting coils. The frequencies of these fields are on the order of a few kilohertz or less. Some studies suggest that ELF fields might have detrimental health effects on humans exposed to them for long periods of time. The claims vary from increased risk of cancer to premature births and miscarriages. However, as of this writing, conclusive proof has yet to be obtained that ELF fields are harmful at the levels encountered by computer users.

The ELF fields surrounding a CRT display tend to be stronger off the sides of the CRT than directly in front of it or behind it. The fields diminish rapidly in intensity with increasing distance from the CRT. As a general rule, computer users should sit at least 18 inches away from a CRT display.Side-by-side workstations should be at least five feet apart.The se considerations are important for visual comfort and"breathing room" as much as for minimizing the potential risk posed by ELF fields.

This was last updated in December 2007

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