Glossary of Light Related Terms

aberration

a flaw in a mirror or lens causing rays of light from a single point to fail to focus at a single spot in space

amplitude

the greatest deviation from equilibrium (center or zero) of a wave

astigmatism

an aberration, or flaw, in a mirror or lens that causes the image of a point to blur into a line

complementary color

within light, two colors that combine to form white light

diffuse reflection

the reflection of rays from a rough surface. The reflected rays do not leave at set angles, so they are scattered

dispersion

the spreading of light into a spectrum of color. The variation in the speed of a periodic wave due to its wavelength or frequency

electromagnetic wave

a wave consisting of oscillating electric and magnetic fields. In a vacuum electromagnetic waves travel at the speed of light

emission spectrum

the collection of discrete wavelengths emitted by atoms that have been excited by heating or by electric currents

focal length

the distance from a mirror or the center of a lens to its focal point

focal point

the location at which a mirror or a lens focuses rays parallel to the optic axis or from which the rays appear to diverge

hologram

a three-dimensional record of visual information

holography

the photographic process for producing three-dimensional images

laser

an acronym for light amplification by stimulated emission of radiation. A device that uses stimulated emissions to produce a coherent beam of electromagnetic radiation

light ray

a line that represents the path of light in a given direction

longitudinal wave

a wave that vibrates in a direction parallel to the path of the wave

normal

an imaginary line perpendicular to a surface; used in determining the direction taken by reflected or refracted light

photoelectric effect

the ejection of electrons from metallic surfaces by illuminating light

polarized

a property of a transverse wave when its vibrations are all in a single plane

quantum

the smallest unit of a discrete property. For instance, the quantum of light is the photon

real image

an image formed by the convergence of light

reflecting telescope

A type of telescope that focuses light with a curved mirror

reflection law

The angle of reflection (measured relative to the normal to the surface) is equal to the angle of incidence ray, the reflected ray, and the normal all lie in the same plane

refracting telescope

a type of telescope that focuses light with a lens

refraction

the bending of light that occurs at the interface between two transparent media. It occurs when the speed of light changes

retroreflectors

three flat mirrors at right angles to each other that reflect light back to its source

spherical aberration

a defect caused by grinding that surface of a lens or mirror to a spherical rather that a parabolic shape

transverse wave

a wave in which the vibrations of the medium are perpendicular to the direction the wave is moving

virtual image

the image formed when light only appears to come from the location of the image

wave

the movement of energy from one place to another without any accompanying matter

wavelength

the shortest repetition length for a periodic wave. For example, it is the distance from crest to crest or from trough to trough