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light : electromagnetic radiation of any wavelength that travels in a vacuum with a speed of 299,792,458 meters (about 186,000 miles) per second; specifically : such radiation that is visible to the human eye. — Webster   See also OneLook


Roget’s II (, Merriam-Webster Thesaurus, Visuwords


Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to visible light, which is the visible spectrum that is visible to the human eye and is responsible for the sense of sight. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), or 4.00 × 10−7 to 7.00 × 10−7 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths). This wavelength means a frequency range of roughly 430–750 terahertz (THz).

The term “light” may also refer more broadly to electromagnetic radiation of any wavelength, whether visible or not. In this sense, gamma rays, X-rays, microwaves and radio waves are also light. The primary properties of light are intensity, propagation direction, frequency or wavelength spectrum and polarization. Its speed in a vacuum, 299 792 458 metres a second (m/s), is one of the fundamental constants of nature. Like all types of electromagnetic radiation, visible light propagates by massless elementary particles called photons that represents the quanta of electromagnetic field, and can be analyzed as both waves and particles. — Wikipedia

Light (Encyclopædia Britannica)


Light (WolframAlpha)



Optical illusion (also called a visual illusion) is an illusion caused by the visual system and characterized by a visual percept that arguably appears to differ from reality. — Wikipedia

Zach King’s Magic Tricks and illusions (Youtube Playlist)
Zach King (Wikipedia)

Optical Illusions (Exploring the Science of Light, Optical Society of America)
Optical Illusions and How They Work (American Museum of National History
148 Optical Illusions & Visual Phenomena (Michael Bach)




Optics is the branch of physics that studies the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties. — Wikipedia

Optics (Encyclopædia Britannica)
Optics (Eric Weisstein’s World of Physics, Wolfram Research)
Optics (WolframAlpha)

Electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies. The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from below one hertz to above 1025 hertz, corresponding to wavelengths from thousands of kilometers down to a fraction of the size of an atomic nucleus. This frequency range is divided into separate bands, and the electromagnetic waves within each frequency band are called by different names; beginning at the low frequency (long wavelength) end of the spectrum these are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays at the high-frequency (short wavelength) end. The electromagnetic waves in each of these bands have different characteristics, such as how they are produced, how they interact with matter, and their practical applications. — Wikipedia

spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Historically, spectroscopy originated as the study of the wavelength dependence of the absorption by gas phase matter of visible light dispersed by a prism. Spectroscopy, primarily in the electromagnetic spectrum, is a fundamental exploratory tool in the fields of physics, chemistry, and astronomy, allowing the composition, physical structure and electronic structure of matter to be investigated at the atomic, molecular and macro scale, and over astronomical distances. — Wikipedia

Molecules and Light (PHET Interactive Simulations, University of Colorado)

Spectroscopy (Encyclopædia Britannica)

Photonics is the science and application of light (photon) generation, detection, and manipulation through emission, transmission, modulation, signal processing, switching, amplification, and sensing. Though covering all light’s technical applications over the whole spectrum, most photonic applications are in the range of visible and near-infrared light. — Wikipedia


Laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word “laser” is an acronym for light amplification by stimulated emission of radiation. A laser differs from other sources of light in that it emits light which is coherent. Spatial coherence allows a laser to be focused to a tight spot, enabling applications such as laser cutting and lithography. Spatial coherence also allows a laser beam to stay narrow over great distances (collimation), enabling applications such as laser pointers and lidar (light detection and ranging). Lasers can also have high temporal coherence, which allows them to emit light with a very narrow spectrum. Alternatively, temporal coherence can be used to produce ultrashort pulses of light with a broad spectrum but durations as short as a femtosecond. — Wikipedia

Minute Physics (YouTube)

SmarterEveryDay (YouTube Channel)

Laser (Encyclopædia Britannica)
Lasers (Eric Weisstein’s World of Physics, Wolfram Research)



Optics Campaigns (Kickstarter)
Optics Campaigns (Indiegogo)


Optics Gifts (Zazzle)




Vintage Lighting Films (YouTube Playlist, Illuminating Engineering Society)
Illuminating Engineering Society (Official Site)
Illuminating Engineering Society (YouTube Channel)
Illuminating Engineering Society (Wikipedia)

Objectivity (Royal Society, YouTube Channel)
Objectivity (Royal Society)

Optics Timeline (Exploring the Science of Light, Optical Society of America)
Optics Timeline (Optics4Kids)


The Museum of Optics
Optical Heritage Museum


Library of Congress # QC350 Light (UPenn Online Books)

WorldCat, Library of Congress, UPenn Online Books, Open Library




Light & Optics (Physics4Kids)

Exploring the Science of Light! (Optical Society of America)
Explore the Electromagnetic Spectrum (Space Place, NASA)
Light & Radiation (PHET Interactive Simulations, University of Colorado)

MERLOT: Multimedia Educational Resource for Learning and Online Teaching
OER Commons: Open Educational Resources


Optical Materials and Devices (MITx)

Optics (edX)
Spectroscopy (edX)
Spectroscopy (MIT OpenCourseWare)



Careers in Optics and Photonics (Optica)

Optometrists (CareerOneStop, U.S. Department of Labor, Employment and Training Administration)
Photonics Engineers (CareerOneStop, U.S. Department of Labor, Employment and Training Administration)


International Society for Optics and Phontonics (SPIE)
Illuminating Engineering Society
IEEE Photonics Society


Optics News (SPIE)
Nature of Light (Science Daily)
Optics and Photonics News (
Optics (NPR Archives)


Light (ISBNdb)



Light (




We Are One Step Closer to a Lightsaber (Darren Orf, Popular Mechanics
Scientists Catch Up With Jedi in Understanding Light (Richard Adhikari, TechNewsWorld)


Mirrors (Tim Hunkin, The Rudiments of Wisdom Encyclopedia)
Lenses (Tim Hunkin, The Rudiments of Wisdom Encyclopedia)
Lasers (Tim Hunkin, The Rudiments of Wisdom Encyclopedia)



Each atom absorbs unique light,
Leaving lines that are black as the night.
This absorption occurs
At the bits it prefers,
So the rest of the spectrum stays bright. — DenmarK, absorption spectrum

OEDILF: The Omnificent English Dictionary In Limerick Form


A Capella Science (Official site)
A Capella Science (YouTube Channel)
Tim Blais (Wikipedia)

Light (Song Lyrics)



Here are links to pages about closely related subjects.

Knowledge Realm


Law (Constant) Relativity
Force Gravity, Electromagnetism (Light, Color)
Matter (Microscope) Molecule, Atom (Periodic Table), Particle

Universe (Astronomical Instrument)
Galaxy Milky Way, Andromeda
Planetary System Star, Brown Dwarf, Planet, Moon

Our Neighborhood
Solar System Sun
Terrestrial Planet Mercury, Venus, Earth (Moon), Mars
Asteroid Belt Ceres, Vesta
Jovian Planet Jupiter, Saturn, Uranus, Neptune
Trans-Neptunian Object
Kuiper Belt Pluto, Haumea, Makemake
Scattered Disc Eris, Sedna, Planet X
Oort Cloud Etc. Scholz’s Star
Small Body Comet, Centaur, Asteroid


1.   The resources on this page are are organized by a classification scheme developed exclusively for Cosma.