ABSTRACT
In classical electromagnetic theory, light is treated as electromagnetic radiation, consisting of both electric and magnetic vector waves. The wave characteristics are described by frequency (υ), wavelength (λ), and velocity (c). Light travels in vacuum at a speed of 300,000 km/s, regardless of its frequency or wavelength. However, in a medium, light travels slower than in vacuum; its actual speed depends on the type of waves or wavelengths and the property of the medium. As the speed of light changes from one medium to another, the light no longer travels in a straight direction. Instead, the light changes its traveling direction after it enters the second medium. This important phenomenon is called refraction, which contributes to light scattering and propagation in food and biological materials and will be further discussed in a later section and also in Chapter 2.
