What is EMF

Electromagnetic radiation (EMR) is energy in waves (like visible light), emitted from a source. It travels at the speed of light

This energy is both electric and magnetic. The waves alternate rapidly, from positive to negative in electrical terms, and from North to South pole in magnetic terms.

Electricity and magnetism are very closely related in nature. For example, when an alternating magnetic wave penetrates a body (including yours!) an alternating electric current will flow inside that body.

Electromagnetic radiation from a source penetrates the surrounding area, creating an electromagnetic field (EMF). This EMF is strongest at the source, and weakens with increasing distance until it becomes too small to measure.

The powerful effect of distance

A strong EMF can be due to a powerful source of radiation far away, or a weak radiation source very close by.

That is why the EMF your body experiences from your cellphone (when you make a call) is much stronger than the EMF you experience from the cell phone tower.

(Although the cell phone is a weak radiation source, it is located very close to your person, whereas the much more powerful cell tower is located thousands of times further away).


EMR Penetration

Some forms of electromagnetic radiation are more penetrating than others.

Visible light for example, can penetrate certain materials (like air, water and glass) but will not penetrate brick walls or metal sheets. It doesn’t penetrate far into human flesh.

X-rays will penetrate human flesh and leave an image on a photographic plate. Gamma rays will travel straight through that photographic plate!

Some common electromagnetic radiation found in everyone’s home, is very penetrating.

Extremely Low Frequency (ELF) radiation (such as from a mains electrical appliance) will actually penetrate concrete pillars and metal sheets, and of course, human flesh and bone.

But radiation from an electrical appliance is relatively weak, so the measurable EMF extends for a short distance only, usually just a few feet.

Penetration is a key issue when it comes to EMR health effects.


Some important properties of electromagnetic radiation are Frequency, Wavelength and Intensity. (If you are not interested in the technical details, you can skip these sections. Catch up with us again at Electromagnetic Spectrum)


The frequency of a wave tells us how fast the wave oscillates in cycles per second, also called Hertz (or Hz). A cycle is one oscillation of the wave (one peak and one trough).

The range of all frequencies of electromagnetic radiation is collectively known as the Electromagnetic Spectrum.


The wavelength of a wave is the distance between two successive wave crests. Wavelength is inversely proportional to frequency – the higher the frequency, the shorter the wavelength.

Electromagnetic wavelengths of interest to us span a huge range – from about 5000 km (long wave) to less than a billionth of a meter (gamma rays).


In practical terms, the intensity or strength of an electromagnetic field at any particular point depends upon

    • the amount of electrical and magnetic energy radiating from its source
    • the distance from that source
    • the extent to which the radiation has been absorbed (or blocked, or shielded).

EMF Measurement

The electric field and magnetic field components of the EMF can be separately measured.

Electrical field strength can be measured in volts per metre (V/m) or as power density in milliwatts per square centimeter (mW/cm2).

Magnetic fields can be quantified in milligauss (mG) or microTesla (1 microTesla = 10 milliguass).


The energy of ionizing radiation (explained below) is often quantified in electron volts (eV) but the absorbed radiation dose is measured in grays (Gy).

Different kinds of ionizing radiation have more or less effect on human tissue. So the expected biological effect of a dose of absorbed radiation is measured in sieverts (Sv) or more usually, millisieverts (mSv).

Electromagnetic Spectrum

In the electromagnetic spectrum, frequencies range from less than 20 Hz at the low  end to 1,000,000,000,000,000,000,000,000 Hz at the high end. Scientists write that as 1024 Hz , because it saves a lot of time!

The visible light spectrum is a portion of the electromagnetic spectrum. Visible light ranges from 1014Hz to 1015Hz. Here is the complete spectrum, with approximate frequency ranges:

Type of Radiation

Frequency Range               (Hz)

   From            To

Extremely Low Frequency (ELF)




Very Low Frequency (VLF)



Radio Frequency (RF)



Microwaves (MW)



Infra-red (IR)



Visible light (from red to violet)




Ultra-violet (UV)






Gamma Rays



Although we divide it up into different divisions and give them names (based on their properties), the electromagnetic spectrum is continuous.

As the frequency increases, waves gradually change their properties, just as the colours of a rainbow gradually blend from one colour to the next.

A good way of visualizing the EM spectrum is to think of all these types of rays as different colours, of which we can only see a few (those in the visible light range). The other “colours” are all invisible to us.

They are all just different forms of the same stuff – raw energy riding on a wave.

They can all be harmful to a person’s health because they penetrate your body and interact with molecules in your cells.

Let’s look at the properties of some of these kinds of waves in a little more detail.

Low Frequency EMFs (ELF and VLF)

The ELF band includes the important power-line frequency (60 Hz in US and 50 Hz elsewhere) which contributes greatly to our electromagnetic pollution. Power-lines, house-wiring and electrical appliances all create this kind of EMF.

An electrical appliance may emit electromagnetic radiation at more than one frequency. For example, a washing machine on spin cycle could emit an EMF of 60 Hz (the supply frequency) as well as an EMF related to the speed of the electric motor driving the spinning drum.

At these low frequencies it is still possible to separate the electrical and magnetic components of the EMF. (At higher frequencies it can’t be done).



An electric field may be created by the electric charge in the supply wire to an electrical appliance, even though the appliance itself may not be switched on.

When the appliance is switched on and a current actually flows through it, the appliance (and its supply wire) will generate a magnetic field as well as an electric field. (A magnetic field is always generated when an alternating electrical current flows).

For low frequency EMFs, the electric field is easily shielded, even by flimsy screening. But the magnetic field penetrates most materials, including brick or concrete walls. It has no trouble penetrating a human body.

Because of this penetration, the magnetic field is the more important component of low frequency EMF, so this is the component that is usually measured – in milligauss (mG).

Radio Frequency EMF

The radio frequency band includes AM and FM radio and TV (VHF) transmissions.

For this type of EMF, the magnetic field strength is proportional to the electric field strength. Both are equally penetrating, so you can’t separate one from the other. If you know the magnetic field strength, you can calculate the electric field strength, and vice versa.

It’s easier to measure the electric field, so the intensity is quantified in Volts per metre (V/m).

Microwave EMF

The microwave band includes radiation from cell phones, cell phone towers, other communications systems and microwave ovens.

As for Radio waves, the magnetic field strength is proportional to the electric field strength, so we measure the electric field strength in Volts per metre (V/m)

These are high energy waves which penetrate deep into the human body, just as the microwaves in your oven penetrate deep into your food.

Wave modulation

Electromagnetic waves may be modulated to encode a digital or analog signal. This is how radio and microwave frequencies can be used to transmit audio or video information.

Radio and TV transmissions, as well as cellphone communications, all use a modulated signal on top of a basic ‘carrier’ wave.

In the case of these modulated waves, it appears that the encoded signal itself (apart from its carrier wave) is also a possible source of biological effects. 

Nuclear Radiation (also called Ionizing Radiation)

The radiation from the top end of the frequency range (high ultra-violet, x-rays and gamma rays) has so much energy that when it collides with an electron in a molecule, it can knock that electron right out of its orbit.

This upsets the electrical charge of the molecule, and creates a positively charged molecule instead, called an ion. So this kind of radiation is called ionizing.

Because of their electrical charge, ions are very reactive chemically, and they quickly connect with other molecules nearby, trying to steal an electron to replace the one they lost.

If this happens to a molecule inside your body, it’s called a “free radical”. Just think of it as a molecular terrorist.

As you can imagine, too many free radicals mess up your biology, especially if they damage molecules inside your cells’ DNA.

Nuclear radiation is the most dangerous kind of electromagnetic radiation (although they can all be dangerous). So it’s quite important to make sure that you are not exposed to more than your body can handle!

Radiation emitted during nuclear power station accidents, is ionizing radiation.

You can also find it in x-ray machines, and in various industrial processes, as well as in nature (usually in small quantities).

Natural radiation is shielded by Earth’s atmosphere

In general, Earth’s atmosphere protects us by absorbing most of the electromagnetic frequencies present in the cosmos, except for lower frequency radio waves and visible light rays. This is the environment in which we evolved. So 

Animals and humans evolved in an environment where many wavelengths were either not present at all, or were fleetingly present at low intensity.

That is why we have not developed protective mechanisms against them.

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