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182 Algae: Anatomy, Biochemistry, and Biotechnology

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FIGURE 5.1 The electromagnetic spectrum from g-rays (10 26 ) to radio waves (10 ).

wavelength. Frequency is usually measured in cycles per second or Hertz (Hz). Thus, longer wave-
lengths correspond to lower frequency radiation and shorter wavelengths correspond to higher fre-
quency radiation. A wave is characterized by a velocity (the speed of light) and phase. If two waves
arrive at their crests and troughs at the same time, they are said to be in phase.
An electromagnetic wave, although it carries no mass, does carry energy. The amount of energy
carried by a wave is related to the amplitude of the wave (how high is the crest). A high energy wave
is characterized by high amplitude; a low energy wave is characterized by low amplitude. The
energy transported by a wave is directly proportional to the square of the amplitude of the wave.
The electromagnetic wave does not need any medium for its sustaining; unlike the sound, light
can travel in the vacuum.

HOW LIGHT BEHAVES
During traveling light waves interact with matter. The consequences of this interaction are that the
waves are scattered or absorbed. In the following, we describe the principal behaviors of light.

SCATTERING

Scattering is the process by which small particles suspended in a medium of a different density
diffuse a portion of the incident radiation in all directions. In scattering, no energy transformation
results, there is only a change in the spatial distribution of the radiation (Figure 5.2).

FIGURE 5.2 Light interaction with matter: the scattering process.