Fundamentals of Optics

Light, Electromagnetic Spectrum

“…Michelson also carried out experiments to measure the speed of light by improving on Galileo's echo technique by replacing men carrying lanterns with a series of mirrors and a telescope. By adjusting the rotation speed of the mirrors, he could observe the light in the telescope, and from the rotation of the mirror and the known distance traveled by the light, he was able to determine the speed of light to about six significant figures [2]. Presently, the speed of light is the most accurately known fundamental constant of nature.…”

“…However, some properties of light, such as the fussiness produced when light passes around obstacles or through openings (diffraction), needed a different model of light where it behaved like a type of wave or propagating disturbance. In the early 1700s, both the particle and wave models of light prevailed with Sir Isaac Newton being a staunch supporter of the particle theory and others, such as the Dutch physicist, Christiaan Huygens, being proponents of the wave theory [2]. But, in the early 1800s, when the English physician Thomas Young showed that light diffracted and interfered to produce fringes when it passed through a double slit, the wave model of light became the accepted theory.…”

“…However, light is very different from other types of waves. In 1881, in one of the most famous experiments with light, Michelson and Morley tried to measure the rotational motion of the earth in this luminiferous ether [2]. However, they found that the light did not travel at different speeds for different paths.…”

“…At the end of the nineteenth century, the particle theory of light was revived by Einstein, who used particle behavior and a new type of theory -quantum physics -to explain the photoelectric effect. It is now widely accepted that light exhibits all three of these behaviors: particle, wave, and quantum, which are used to explain all known properties of light [2].…”

“…When it is used to describe a light stimulus, the International Lighting Vocabulary [1] gives the following two definitions: (1) It is a characteristic of all sensations and perceptions that is specific to vision, and (2) it is radiation that is considered from the point of view of its ability to excite the human visual system, i.e., it is limited to electromagnetic radiation with wavelengths in the visible spectral region between approximately 380 and 780 nm.…”