Fokko Jan Dijksterhuis, Lenses and Waves: Christiaan Huygens and the Mathematical Science of Optics in the 17th Century, Kluwer Academic Publishers, 2004, ISBN 1-4020-2697-8 Seymour: Hello! Seymour Science here… today’s episode is all about where light comes from… with my expert friend, Albert! Light is measured with two main alternative sets of units: radiometry consists of measurements of light power at all wavelengths, while photometry measures light with wavelength weighted with respect to a standardized model of human brightness perception. Photometry is useful, for example, to quantify Illumination (lighting) intended for human use.

The effective velocity of light in various transparent substances containing ordinary matter, is less than in vacuum. For example, the speed of light in water is about 3/4 of that in vacuum. Narinder Kumar (2008). Comprehensive Physics XII. Laxmi Publications. p. 1416. ISBN 978-81-7008-592-8. Reference Solar Spectral Irradiance: Air Mass 1.5". Archived from the original on 12 May 2019 . Retrieved 12 November 2009. Main article: Refraction Due to refraction, the straw dipped in water appears bent and the ruler scale compressed when viewed from a shallow angle.

Singh, S. (2009). Fundamentals of Optical Engineering. Discovery Publishing House. ISBN 978-8183564366. Liang, Qi-Yu; et al. (16 February 2018). "Observation of three-photon bound states in a quantum nonlinear medium". Science. 359 (6377): 783–786. arXiv: 1709.01478. Bibcode: 2018Sci...359..783L. doi: 10.1126/science.aao7293. PMC 6467536. PMID 29449489.

Certain substances produce light when they are illuminated by more energetic radiation, a process known as fluorescence. Some substances emit light slowly after excitation by more energetic radiation. This is known as phosphorescence. Phosphorescent materials can also be excited by bombarding them with subatomic particles. Cathodoluminescence is one example. This mechanism is used in cathode-ray tube television sets and computer monitors.Light moves in a straight line. The straight line path is often drawn as a ray. Humans can only see rays of light traveling directly into the eyes. Ray diagrams are used to illustrate light traveling from one place to another. A beam of light can be thought of as a set of light rays. Main article: Speed of light Beam of sun light inside the cavity of Rocca ill'Abissu at Fondachelli-Fantina, Sicily The weakness of the wave theory was that light waves, like sound waves, would need a medium for transmission. The existence of the hypothetical substance luminiferous aether proposed by Huygens in 1678 was cast into strong doubt in the late nineteenth century by the Michelson–Morley experiment. Eventually the modern theory of quantum mechanics came to picture light as (in some sense) both a particle and a wave and (in another sense), as a phenomenon which is neither a particle nor a wave (which actually are macroscopic phenomena, such as baseballs or ocean waves). Instead, modern physics sees light as something that can be described sometimes with mathematics appropriate to one type of macroscopic metaphor (particles) and sometimes another macroscopic metaphor (water waves), but is actually something that cannot be fully imagined. As in the case for radio waves and the X-rays involved in Compton scattering, physicists have noted that electromagnetic radiation tends to behave more like a classical wave at lower frequencies, but more like a classical particle at higher frequencies, but never completely loses all qualities of one or the other. Visible light, which occupies a middle ground in frequency, can easily be shown in experiments to be describable using either a wave or particle model, or sometimes both. Light with a wavelength shorter than violet is called ultraviolet light. X-rays and gamma rays are forms of light with even shorter wavelengths than ultraviolet. Light with a wavelength longer than red is called infrared light. Radio waves are a form of electromagnetic radiation with a wavelength longer than infrared light. The microwaves that are used to heat food in a microwave oven are also a form of electromagnetic radiation. Our eyes cannot see those kinds of energy, but there are some cameras that can see them. The various forms of light, both visible and invisible are the electromagnetic spectrum.

The behavior of EMR depends on its wavelength. Higher frequencies have shorter wavelengths and lower frequencies have longer wavelengths. When EMR interacts with single atoms and molecules, its behavior depends on the amount of energy per quantum it carries. The other main properties of light are intensity, polarization, phase and orbital angular momentum. Michelson, A.A. (January 1927). "Measurements of the velocity of light between Mount Wilson and Mount San Antonio". Astrophysical Journal. 65: 1. Bibcode: 1927ApJ....65....1M. doi: 10.1086/143021. 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. Some species of animals generate their own light, a process called bioluminescence. For example, fireflies use light to locate mates and vampire squid use it to hide themselves from prey. On the other hand, the Vaisheshika school gives an atomic theory of the physical world on the non-atomic ground of ether, space and time. (See Indian atomism.) The basic atoms are those of earth ( prthivi), water ( pani), fire ( agni) and air ( vayu) Light rays are taken to be a stream of high velocity of tejas (fire) atoms. The particles of light can exhibit different characteristics depending on the speed and the arrangements of the tejas atoms. [ citation needed]

Video transcript for ‘Light’

It has a wavelength which can be seen by the human eye. [1] Animals can also see light. Light makes up a small part of both the electromagnetic spectrum and radiation given off by stars like the sun. The study of light is known as optics. When light hits an opaque object, it makes a shadow. When light hits a transparent object, it passes through it almost completely without making a shadow. Use a protractor to measure angles of incidence from this normal of 10°, 20°, 30°, 40°, 50°, 60° and 70°. Draw in the incident rays corresponding to these angles and label them A, B, C.... Record these angles of incidence in a suitable table. NASA team successfully deploys two solar sail systems". NASA. 9 August 2004. Archived from the original on 14 June 2012 . Retrieved 30 May 2008.