index of refraction

noun

, Optics.

1. a number indicating the speed of light in a given medium as either the ratio of the speed of light in a vacuum to that in the given medium absolute index of refraction or the ratio of the speed of light in a specified medium to that in the given medium relative index of refraction. : n

index of refraction

noun

1. See refractive index
   another name for refractive index

index of refraction

1. A measure of the extent to which a substance slows down light waves passing through it. The index of refraction of a substance is equal to the ratio of the velocity of light in a vacuum to its speed in that substance. Its value determines the extent to which light is refracted when entering or leaving the substance.

Word History and Origins

Origin of index of refraction¹

First recorded in 1820–30

Example Sentences

He'd gotten an index-of-refraction reading on crystals too small to be seen except through a microscope.

From Project Gutenberg