The eye and visual pathways

This chapter describes light as a component of the electromagnetic spectrum, wherein the human eye responds to radiation with wavelengths between about 380 nm to 750 nm. The chapter talks about particles that carry radiation called light. These particles are known as photons. They have no mass or electric charge but carry a very small amount of energy that depends on the wavelength of light. Although the eye is able to respond to light of intensities over 15 orders of magnitude, the range of light intensities that are normally encountered in daily life is somewhat smaller. The chapter looks at different phases of vision in bright, low-level light, and dark conditions. These conditions are classified as photopic, mesopic, and scotopic. During the day, photopic vision is dominant, but at night, especially in the absence of artificial light, the ability to see depends entirely on scotopic vision.