First Principles - Sustainable Design: The Science of Sustainability and Green Engineering - page 49

Natural and many anthropogenic sources produce EMR energy in the form
of waves, which are oscillating energy fields that can interact with an organism's
cells. The waves are described according to their wavelength and frequency
and the energy they produce. Wave frequency is the number of oscillations that
pass a fixed point per unit of time, measured in cycles per second (cps) [1 cps =

1 hertz (Hz)]. Thus, the shorter the wavelength, the higher the frequency. For
example, the middle of the amplitude-modulated (AM) radio broadcast band
has a frequency of 1 million hertz (1 MHz) and a wavelength of about 300
m. Microwave ovens use a frequency of about 2.5 billion hertz (2.5 GHz) and
a wavelength of 12 cm. So the microwave, with its shorter wavelength, has a
much higher frequency.
An EMR wave is made of tiny packets of energy called photons . The energy
in each photon is directly proportional to the frequency of the wave. So
the higher the frequency, the more energy there will be in each photon.
Cellular material is affected in part by the intensity of the field and partly
by the quantity of energy in each photon. At low frequencies EMR waves
are known as electromagnetic fields , and at high frequencies EMR waves are
referred to as electromagnetic radiations . Also, the frequency and energy determine
whether an EMR will be ionizing or nonionizing radiation. Ionizing radiation
consists of high-frequency electromagnetic waves (e.g., x-rays and gamma rays)
having sufficient photon energy to produce ionization (producing positive and
negative electrically charged atoms or parts of molecules) by breaking bonds
of molecules. The general term nonionizing radiation is the portion of the
electromagnetic spectrum where photon energies are not strong enough to
break atomic bonds. This segment of the spectrum includes ultraviolet (UV)
radiation, visible light, infrared radiation, radio waves, and microwaves, along
with static electrical and magnetic fields. Even at high intensities, nonionizing
radiation cannot ionize atoms in biological systems, but such radiation has
been associated with other effects, such as cellular heating, changes in chemical
reactions and rates, and the induction of electrical currents within and between
cells.
EMR is an enigma. At certain wavelengths and frequencies it is beneficial
(warmth and light), but at other wavelengths and frequencies it causes harm
to an organism. A mammal may respond to EMR by increasing blood flow
in the skin in response to slightly greater heating from the sun. EMR may
also induce other positive health effects, such as the sun's role in helping the
body produce vitamin D. Unfortunately, certain direct or indirect responses to
EMR may lead to adverse effects, including skin cancer.
The data supporting UV radiation as a contaminant are stronger than those
associated with the more subtle fears that sources such as high-energy power
transmission lines and cell phones may be producing health effects. The World