What is Electromagnetic Radiation?
The transmission of electrical energy through wires, the broadcasting of radio signals and the phenomenon of visible light are examples of electromagnetic radiation (EMR).
EMR always consists of both an electrical field and a magnetic field.
It occurs in a wide range of frequencies, spanning what is called the electromagnetic spectrum.
At the high end is cosmic radiation. This background radiation affects everyone and varies depending on location.
A serious type of cosmic radation comes from the sun, where long exposure can cause harmful effects. We are protected from the sun’s radiation by the earth’s atmosphere and the ozone layer.
At the low end is household electricity. The lower electromagnetic frequencies are used to generate electricity and for all associated electrical products, including all electronic communication systems and electrical appliances.
Electromagnetic radiation (EMR) is often called an electromagnetic field (EMF) when it falls within the lower frequencies. Both EMR and EMF are commonly used to mean the same thing.
Electricity is the most common source of power throughout the world because it is easily generated and transmitted to where it is needed. As electricity moves through wires and machines, it produces EMF.
The power grids of nations consist of electrical generation, transmission and distribution facilities. As electricity is sent along the wires of the power grid, EMF is created.
In cities, primary electric power distribution lines run across the top of utility poles and feed secondary transformers, which are then connected to the electric power meters of buildings.
Once electricity is delivered to the user, it continues to produce EMF throughout the wiring systems of offices, homes, schools, factories and other structures.
The appliances and electrical equipment connected to these wiring systems produce their own EMF as well.
In the workplace the generators of EMF include computers, mobile phones, fluorescent lights, printers, scanners, telephone switching systems, electrical instruments, motors and other electrical devices.
In homes, the immediate sources of EMF include electric blankets, electric water bed heaters, hairdryers, electric shavers, televisions, sound systems, air conditioners, lighting, telephone answering machines, mobile and cordless phones, refrigerators, blenders, portable electric heaters, boilers, clothes washers and dryers, electric ovens, kitchen appliances, vacuum cleaners and microwave ovens.
EMF is not only produced by electricity moving through wires or machines, but it is the nature of all television and satellite transmissions, as well as radio and microwave communication systems, including mobile phones.
Transportation methods such as automobiles, trucks, airplanes, electrical and magnetic trains and subway systems are significant sources of EMF.
More than one source of EMF in proximity to other sources will produce overlapping fields in the same area. Any home or office in a built-up area will be saturated by a variety of interpenetrating EMF from a variety of sources.
Do Power Lines Produce EMR?
To be an effective radiation source, an antenna must have a length comparable to its wavelength. Power-frequency sources are clearly too short compared to their wavelength (5,000 km) to be effective radiation sources. Calculations show that the typical maximum power radiated by a power line would be less than 0.0001 microwatts / Cm.2, compared to the 0.2 microwatts/Cm.2 that a full moon delivers to the Earth’s surface on a clear night.
This is not to say that there is no loss of power during transmission. There are sources of loss in transmission lines that have nothing to do with “radiation” (in the sense as it is used in electromagnetic theory). Much of the loss of energy is a result of resistive heating; this is in sharp contrast to radio frequency and microwave antennas, which “lose” energy to space and environment by radiation.
Likewise, there are many ways of transmitting energy that do not involve radiation; electric circuits do it all the time.
What sort of power-frequency fields are common in residences and workplaces?
In the US magnetic fields are often still measured in Gauss (G) or milligauss (mG), where:
1,000 mG = 1 G.
In the rest of the world and in the scientific community, magnetic fields are measured in tesla (T), where:
10,000 G = 1 T
1 G = 100 microT (μT)
1000 nanoT (nT) = 1 microT = 10 mG
Recommended safety levels range from 50 nT to 250 nT as the maximum exposure – with 100 nT or 1.0 mG as a preferred standard. Adverse biological effects have been found at 250 nT or 2.5 mG.