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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.

  • Shedding light on -- and through -- 2D materials
    on September 24, 2018 at 4:39 pm

    Scientists use a computational method to calculate the optical properties of two-dimensional materials. Their work promises to simplify the process of identifying the right materials for next-generation optoelectronic devices. […]

  • Smaller, faster and more efficient modulator sets...
    on September 24, 2018 at 3:27 pm

    A research team has successfully fabricated a tiny on-chip lithium niobate modulator, an essential component for the optoelectronic industry. The modulator is smaller, more efficient with faster data transmission and costs less than traditional ones. […]

  • Researchers teach computers to see optical...
    on September 21, 2018 at 3:34 pm

    By making a neural-network computer model that can be fooled by optical illusions like humans, the researchers advanced knowledge of the human visual system and may help improve artificial vision. […]

  • Lighting it up: A new non-toxic, cheap, and...
    on September 19, 2018 at 5:33 pm

    Scientists have designed a novel photoluminescent material that is cheap to fabricate, does not use toxic starting materials, and is very stable, enhancing our understanding of the quantic nature of photoluminescence. […]

  • How long does a quantum jump take?
    on September 19, 2018 at 5:33 pm

    Quantum jumps are usually regarded to be instantaneous. However, new measurement methods are so precise that it has now become possible to observe such a process and to measure its duration precisely -- for example the famous 'photoelectric effect', first described by Albert Einstein. […]

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

  • Smaller, faster and more efficient modulator sets...
    on September 24, 2018 at 3:00 pm

    A research team comprising members from City University of Hong Kong (CityU), Harvard University and a renowned information technologies laboratory has successfully fabricated a tiny on-chip lithium niobate modulator, an essential component for the optoelectronic industry. The modulator is smaller, more efficient with faster data transmission, and costs less. The technology is set to revolutionise the industry. […]

  • On-demand room-temperature single photon...
    on September 21, 2018 at 12:47 pm

    Physicists at The City College of New York have used atomically thin two-dimensional materials to realize an array of quantum emitters operating at room temperature that can be integrated into next generation quantum communication systems. […]

  • Perovskite semiconductors seeing right through...
    on September 21, 2018 at 12:26 pm

    From observing celestial objects to medical imaging, the sensitive detection of X-rays plays a central role in countless applications. However, the methods used to detect them have undergone an interesting evolution of their own. […]

  • Researchers determine absolute duration of...
    on September 20, 2018 at 12:30 pm

    The photoelectric effect provides the basis for solar energy and global communications; Albert Einstein described it over a century ago. For the first time, scientists from the Technical University of Munich (TUM), the Max-Planck Institute of Quantum Optics (MPQ), and the TU Wien have now measured the absolute duration of the light absorption and of the resulting photoelectron released from a solid body. […]

  • Fiber optic sensor measures tiny magnetic fields
    on September 19, 2018 at 3:55 pm

    Researchers have developed a light-based technique for measuring very weak magnetic fields, such as those produced when neurons fire in the brain. The inexpensive and compact sensors could offer an alternative to the magnetic resonance imaging (MRI) systems currently used to map brain activity without the expensive cooling or electromagnetic shielding required by MRI machines. […]