4.1 Basic Behavior of Light

Figure 4.1: Waves and visibility rays emanating from a point light source.

Light can be described in three ways that appear to be mutually incompatible:

1. Photons: Tiny particles of energy moving through space at high speeds (no need for quantum mechanics in this book!). This interpretation is helpful when considering the amount of light received by a sensor or receptor.
2. Waves: Ripples through space that are similar to waves propagating on the surface of water, but are 3D. The wavelength is the distance between peaks. This interpretation is helpful when considering the spectrum of colors.
3. Rays: A ray traces the motion of a single hypothetical photon. The direction is perpendicular to the wavefronts (see Figure 4.1). This interpretation is helpful when explaining lenses and defining the concept of visibility.

Fortunately, modern physics has explained how these interpretations are in fact compatible; each is useful in this book.