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Physical Realm
Physical Laws (Constants) Relativity
Matter Molecule, Atom (Periodic Table), Particle
Force Gravity, Electromagnetism (Light, Color)


These are organized by a classification scheme developed exclusively for Cosma. More…



Exploring the Science of Light! (Optical Society of America)


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

OneLook, Free Dictionary, Wiktionary, Urban Dictionary


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 main source of light on Earth is the Sun. Sunlight provides the energy that green plants use to create sugars mostly in the form of starches, which release energy into the living things that digest them. This process of photosynthesis provides virtually all the energy used by living things. Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the development of electric lights and power systems, electric lighting has effectively replaced firelight. Some species of animals generate their own light, a process called bioluminescence. For example, fireflies use light to locate mates, and vampire squids use it to hide themselves from prey.

The primary properties of visible light are intensity, propagation direction, frequency or wavelength spectrum, and polarization, while its speed in a vacuum, 299,792,458 metres per second, is one of the fundamental constants of nature. Visible light, as with all types of electromagnetic radiation (EMR), is experimentally found to always move at this speed in a vacuum.

In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. In this sense, gamma rays, X-rays, microwaves and radio waves are also light. Like all types of electromagnetic radiation, visible light propagates as waves. However, the energy imparted by the waves is absorbed at single locations the way particles are absorbed. The absorbed energy of the EM waves is called a photon, and represents the quanta of light. When a wave of light is transformed and absorbed as a photon, the energy of the wave instantly collapses to a single location, and this location is where the photon “arrives.” This is what is called the wave function collapse. This dual wave-like and particle-like nature of light is known as the wave–particle duality. The study of light, known as optics, is an important research area in modern physics. — Wikipedia

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



Light (WolframAlpha), Optics (WolframAlpha)



Optics is the branch of physics which involves 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.

Most optical phenomena can be accounted for using the classical electromagnetic description of light. Complete electromagnetic descriptions of light are, however, often difficult to apply in practice. Practical optics is usually done using simplified models. The most common of these, geometric optics, treats light as a collection of rays that travel in straight lines and bend when they pass through or reflect from surfaces. Physical optics is a more comprehensive model of light, which includes wave effects such as diffraction and interference that cannot be accounted for in geometric optics. Historically, the ray-based model of light was developed first, followed by the wave model of light. Progress in electromagnetic theory in the 19th century led to the discovery that light waves were in fact electromagnetic radiation.

Some phenomena depend on the fact that light has both wave-like and particle-like properties. Explanation of these effects requires quantum mechanics. When considering light’s particle-like properties, the light is modeled as a collection of particles called “photons”. Quantum optics deals with the application of quantum mechanics to optical systems.

Optical science is relevant to and studied in many related disciplines including astronomy, various engineering fields, photography, and medicine (particularly ophthalmology and optometry). Practical applications of optics are found in a variety of technologies and everyday objects, including mirrors, lenses, telescopes, microscopes, lasers, and fiber optics. — Wikipedia

Encyclopædia Britannica


Scientists & Discovery, Light (Museum Victoria Australia)


How Light Works (HowStuffWorks)



Optics Timeline (Optical Society of America)
A History of Light and Lighting (Bill Williams)


Quotations Page Bartlett’s


The Museum of Optics (University of Arizona)


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




OER Commons: Open Educational Resources



Careers in Optics and Photonics (Optical Society of America)


International Society for Optics and Phontonics (SPIE)
Optical Society of America


International Society for Optics and Phontonics (SPIE)
Nature of Light (Science Daily)
Optics and Photonics News (, Optics (Science 2.0), NPR Archives







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


OEDILF: The Omnificent English Dictionary In Limerick Form


Song Lyrics


More… News latest News from

Optics News -- ScienceDaily Optics. Can light go backwards? Researchers push the limits of our understanding of light. Also see amazing new applications of light energy. Full-text, images, free.

  • Considering disorder and cooperative effects in...
    on February 26, 2021 at 6:54 pm

    Scientists aim to numerically investigative the roles of cooperative effects and disorder in photon escape rates from a cold atomic gas to construct a model that considers the vectorial nature of light. Thus, the study accounts for properties of light, previously neglected.

  • Light-emitting tattoo engineered
    on February 26, 2021 at 5:13 pm

    The technology, which uses organic light-emitting diodes (OLEDs), is applied in the same way as water transfer tattoos. That is, the OLEDs are fabricated on to temporary tattoo paper and transferred to a new surface by being pressed on to it and dabbed with water.

  • Light unbound: Data limits could vanish with new...
    on February 25, 2021 at 4:34 pm

    Researchers have found a new way to harness properties of light waves that can radically increase the amount of data they carry. The new work throws wide open the amount of information that can be multiplexed, or simultaneously transmitted, by a coherent light source.

  • Data transfer system connects silicon chips with...
    on February 24, 2021 at 7:36 pm

    Researchers developed a data transfer link that's slimmer, more energy efficient, and faster than alternatives like USB or fiber optics. The advance could cut energy budgets at data centers and lighten the load for electronics-rich aircraft.

  • Twin atoms: A source for entangled particles
    on February 24, 2021 at 7:34 pm

    One of the most important phenomena in quantum physics is entanglement - used for quantum krypography, quantum computers and many other applications. While it is easy to create pairs of entangled photons, it is much harder to create entangled atoms in a well-defined way. This has now been made possible using an experimental setup.

Optics & Photonics News - Optics, Photonics, Physics News The latest news on Optics and Photonics

  • Considering disorder and cooperative effects in...
    on February 26, 2021 at 5:49 pm

    Whilst a great deal of research has studied the rates of photons escaping from cold atomic gases, these studies have used a scalar description of light leaving some of its properties untested. In a new paper published in EPJ B Louis Bellando, a post-doctoral researcher at LOMA, University of Bordeaux, France, and his coauthors—Aharon Gero and Eric Akkermans, Technion-Israel Institute of Technology, Israel, and Robin Kaiser, Université Côte d'Azur, France—aim to numerically investigative […]

  • How photoblueing disturbs microscopy
    on February 26, 2021 at 2:28 pm

    The latest developments in fluorescence microscopy make it possible to image individual molecules in cells or molecular complexes with a spatial resolution of up to 20 nanometres. However, under certain circumstances, an effect occurs that falsifies the results: the laser light used can cause very reactive oxygen molecules to form in the sample. These can then damage the fluorescent dyes used to such an extent that they no longer fluoresce. Among microscopy experts, this effect is known as […]

  • Light-twisting 'chiral' nanotechnology could...
    on February 26, 2021 at 12:49 pm

    A new approach makes liquid-crystal-like beacons out of harmful amyloid proteins present in diseases such as Type II diabetes.

  • Light unbound: Data limits could vanish with new...
    on February 25, 2021 at 5:06 pm

    Researchers at the University of California, Berkeley, have found a new way to harness properties of light waves that can radically increase the amount of data they carry. They demonstrated the emission of discrete twisting laser beams from antennas made up of concentric rings roughly equal to the diameter of a human hair, small enough to be placed on computer chips.

  • Experiment reveals new options for synchrotron...
    on February 24, 2021 at 4:00 pm

    Accelerator experts from the Helmholtz-Zentrum Berlin (HZB), the German federal metrology institute Physikalisch-Technische Bundesanstalt (PTB) and Tsinghua University in Beijing have used a laser to manipulate electron bunches at PTB's Metrology Light Source so that they emitted intense light pulses having a laser-like character. Using this method, specialized synchrotron radiation sources would potentially be able to fill a gap in the arsenal of available light sources and offer a prototype […]