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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

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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.

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  • Want to catch a photon? Start by silencing the sun
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    Researchers have created a 3D imaging system that uses light's quantum properties to create images 40,000 times crisper than current technologies, paving the way for never-before seen LIDAR sensing and detection in self-driving cars, satellite mapping systems, deep-space communications and medical imaging of the human retina.

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

  • Researchers create new state of light
    on February 25, 2020 at 1:01 pm

    For 20 years, researchers have studied how light rotates around a longitudinal axis parallel to the direction light travels. But could it move in other ways? After two years of research, and thanks to a sabbatical, University of Dayton researchers Andy Chong and Qiwen Zhan became the first to create a new "state of light"—showing it also can rotate around a transverse axis perpendicular to the direction light travels, like a cyclone.

  • Team demos breakthrough in analog image processing
    on February 25, 2020 at 12:39 pm

    A research team of Vanderbilt engineers that includes a scientist at Oak Ridge National Laboratory has demonstrated a new ultrathin filter, based on metamaterials, that allows for analog optical image processing. Their work, Flat Optics for Image Differentiation, appears today in the scientific journal, Nature Photonics.

  • Advancement simplifies laser-based medical imaging
    on February 25, 2020 at 12:37 pm

    Photoacoustic imaging, a technique for examining living materials through the use of laser light and ultrasonic sound waves, has many potential applications in medicine because of its ability to show everything from organs to blood vessels to tumors.

  • A simple retrofit transforms electron microscopes...
    on February 24, 2020 at 6:16 pm

    Researchers at the National Institute of Standards and Technology (NIST) and their collaborators have developed a way to retrofit the transmission electron microscope—a long-standing scientific workhorse for making crisp microscopic images—so that it can also create high-quality movies of super-fast processes at the atomic and molecular scale. Compatible with electron microscopes old and new, the retrofit promises to enable fresh insights into everything from microscopic machines to […]

  • Team discovers new way to control the phase of...
    on February 24, 2020 at 6:04 pm

    Optical manipulation on the nano-scale, or nanophotonics, has become a critical research area, as researchers seek ways to meet the ever-increasing demand for information processing and communications. The ability to control and manipulate light on the nanometer scale will lead to numerous applications including data communication, imaging, ranging, sensing, spectroscopy, and quantum and neural circuits (think LIDAR—light detection and ranging—for self-driving cars and faster […]