BASIC CONCEPTS OF RADIATION - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 4

BASIC CONCEPTS OF RADIATION
DAVID H. SLINEY, ERIN CHANEY
US Army Center for Health Promotion and Preventive Medicine
Aberdeen Proving Ground, MD, USA
1. Introduction
Light is an electromagnetic wave that propagates through space at the
phenomenal velocity of 300 km/s, but it represents only a tiny fraction of what we term
the electromagnetic spectrum as shown in Figure 1. To describe any wave, there are
three basic parameters: frequency, wavelength and velocity of propagation. Since all
electromagnetic waves travel at the velocity of light c, the fundamental relationship is:
c = ȜȞ, where Ȝ is the wavelength in meters (m), and Ȟ is the frequency in Hertz (Hz),
i.e., in wave cycles per second. The wavelength is measured between any two
corresponding points along the wave, as shown in Figure 2. Figure 2 also shows the
orthogonal (right-angle) relationship of the electric vector and magnetic vector of this
electromagnetic wave.
Figure 1. The electromagnetic spectrum.