CHAPTER 1 4Eyes and Vision
Our visual system responds to electromagnetic radiation in the
energy range called visible light—so named because we humans can
see it. Electromagnetic energy can be conceptualized as a vibrat-
ing electromagnetic field (an abstract concept from mathematical
physics) moving (radiating) through space, and is described quan-
titatively as either a frequency of vibration (in cycles per second, or
hertz) or a wavelength (in meters). Visible light is in the energy range
between about 400 and 700 nanometers (nm), a range of energy that
can engage in significant and sustainable (nondamaging) interactions
with molecular and cellular structures in the body.
Electromagnetic energy can also be conceptualized as packets of
energy, called photons. The description of light and other kinds of
electromagnetic energy as simultaneously both a wavelike field and
particle-like photons is profound and was central to the develop-
ment of quantum physics in the early twentieth century.(^)
If radiation is more energetic (shorter wavelength) than visible