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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.

  • Nanomaterials enable dual-mode heating and...
    on December 3, 2020 at 12:27 am

    Engineers have demonstrated a dual-mode heating and cooling device for building climate control that, if widely deployed in the U.S., could cut HVAC energy use by nearly 20 percent. The invention uses a combination of mechanics and nanomaterials to either harness or expel certain wavelengths of light. Depending on conditions, rollers move a sheet back and forth to expose either heat-trapping materials or cooling materials.

  • A hint of new physics in polarized radiation from...
    on December 2, 2020 at 4:45 pm

    Astronomers developed a new method to calibrate detectors to the light from dust in our Galaxy, thereby describing a new physics, with 99.2 percent accuracy, that may show parity symmetry breaking.

  • Scientists invent a new type of microscope that...
    on December 2, 2020 at 2:51 pm

    Researchers invented a new type of microscope called reflective matrix microscope, which uses adaptive optics techniques.

  • AI reduces computational time required to study...
    on December 1, 2020 at 5:41 pm

    Light-induced processes are critical in transformative technologies such as solar energy harvesting, as well as in photomedicine and photoresponsive materials. Theoretical studies of the dynamics of photoinduced processes require numerous electronic structure calculations, which are computationally expensive. Scientists developed machine learning-based algorithms, which reduce these computations significantly.

  • Engineers combine light and sound to see...
    on December 1, 2020 at 1:19 am

    Engineers have developed an airborne method for imaging underwater objects by combining light and sound to break through the seemingly impassable barrier at the interface of air and water.

Optics & Photonics News - Optics, Photonics, Physics News provides the latest news on Optics and Photonics

  • Researchers confront optics and data-transfer...
    on December 3, 2020 at 7:47 pm

    Researchers have developed new 3-D-printed microlenses with adjustable refractive indices—a property that gives them highly specialized light-focusing abilities. This advancement is poised to improve imaging, computing and communications by significantly increasing the data-routing capability of computer chips and other optical systems, the researchers said.

  • Physicists succeed in bringing movement of...
    on December 3, 2020 at 5:13 pm

    Scientists from ITMO, Sheffield University, and the University of Iceland proved that the movement of electrons and photons in two-dimensional materials with hexagonal symmetry, such as graphene, submits to the same laws. Now, the properties of electrons in solids can be modeled with the help of classical optical systems where this task can be solved easier. The article was published in Nature Photonics.

  • Supercharge your microscope: Researchers share...
    on December 3, 2020 at 3:36 pm

    UNSW Sydney researchers have shared step-by-step instructions to empower other scientists to enhance the resolution and stability of single-molecule microscopes.

  • Natural three-dimensional nonlinear photonic...
    on December 2, 2020 at 5:13 pm

    Nonlinear photonic crystals (NPCs) are transparent materials that have a spatially uniform linear susceptibility, yet a periodically modulated quadratic nonlinear susceptibility. These engineered materials are used extensively for studying nonlinear wave dynamics and in many scientific and industrial applications. Over the past two decades, there has been a continuous effort to find a technique that will enable the construction of three-dimensional (3-D) NPCs. Such capability will enable many […]

  • Scientists invent a new type of microscope that...
    on December 2, 2020 at 3:53 pm

    Non-invasive microscopic techniques such as optical coherence microscopy and two-photon microscopy are commonly used for in vivo imaging of living tissues. When light passes through turbid materials such as biological tissues, two types of light are generated: ballistic photons and multiply scattered photons. The ballistic photons travel straight through the object without experiencing any deflection and hence are used to reconstruct the object image. On the other hand, the multiply scattered […]