O'Connor, J J; Robertson, E F (August 2002). "Light through the ages: Ancient Greece to Maxwell". Archived from the original on 19 March 2017 . Retrieved 20 February 2017. Use the ruler to join the incident and emergent rays together with a pencil line. This is the refracted ray. Carefully mark in the angle of refraction, r, between the refracted ray and the normal. NASA team successfully deploys two solar sail systems". NASA. 9 August 2004. Archived from the original on 14 June 2012 . Retrieved 30 May 2008. In February 2018, scientists reported, for the first time, the discovery of a new form of light, which may involve polaritons, that could be useful in the development of quantum computers. [42] [43] Use for light on Earth Barrow, Gordon M. (1962). Introduction to Molecular Spectroscopy (Scanned PDF). McGraw-Hill. LCCN 62-12478.

No single answer to the question “What is light?” satisfies the many contexts in which light is experienced, explored, and exploited. The physicist is interested in the physical properties of light, the artist in an aesthetic appreciation of the visual world. Through the sense of sight, light is a primary tool for perceiving the world and communicating within it. Light from the Sun warms the Earth, drives global weather patterns, and initiates the life-sustaining process of photosynthesis. On the grandest scale, light’s interactions with matter have helped shape the structure of the universe. Indeed, light provides a window on the universe, from cosmological to atomic scales. Almost all of the information about the rest of the universe reaches Earth in the form of electromagnetic radiation. By interpreting that radiation, astronomers can glimpse the earliest epochs of the universe, measure the general expansion of the universe, and determine the chemical composition of stars and the interstellar medium. Just as the invention of the telescope dramatically broadened exploration of the universe, so too the invention of the microscope opened the intricate world of the cell. The analysis of the frequencies of light emitted and absorbed by atoms was a principal impetus for the development of quantum mechanics. Atomic and molecular spectroscopies continue to be primary tools for probing the structure of matter, providing ultrasensitive tests of atomic and molecular models and contributing to studies of fundamental photochemical reactions. In 55 BC, Lucretius, a Roman who carried on the ideas of earlier Greek atomists, wrote that "The light & heat of the sun; these are composed of minute atoms which, when they are shoved off, lose no time in shooting right across the interspace of air in the direction imparted by the shove." (from On the nature of the Universe). Despite being similar to later particle theories, Lucretius's views were not generally accepted. Ptolemy (c. second century) wrote about the refraction of light in his book Optics. [33] Classical India Albert: Hi Seymour! Pleasure to be here! Light is what helps us see things. It can come from different places, like the Sun, or fire, or from electricity in lamps and torches. Light is all around us, like the sunlight in this kitchen…So what happens if we take all that away?

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. Main article: Refraction Due to refraction, the straw dipped in water appears bent and the ruler scale compressed when viewed from a shallow angle.

In the fifth century BC, Empedocles postulated that everything was composed of four elements; fire, air, earth and water. He believed that Aphrodite made the human eye out of the four elements and that she lit the fire in the eye which shone out from the eye making sight possible. If this were true, then one could see during the night just as well as during the day, so Empedocles postulated an interaction between rays from the eyes and rays from a source such as the sun. [31] 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 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.

Video transcript for ‘Light’

Various sources define visible light as narrowly as 420–680 nm [7] [8] to as broadly as 380–800 nm. [9] [10] Under ideal laboratory conditions, people can see infrared up to at least 1,050 nm; [11] children and young adults may perceive ultraviolet wavelengths down to about 310–313 nm. [12] [13] [14] 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. In about 300 BC, Euclid wrote Optica, in which he studied the properties of light. Euclid postulated that light travelled in straight lines and he described the laws of reflection and studied them mathematically. He questioned that sight is the result of a beam from the eye, for he asks how one sees the stars immediately, if one closes one's eyes, then opens them at night. If the beam from the eye travels infinitely fast this is not a problem. [32] Sliney, David H.; Wangemann, Robert T.; Franks, James K.; Wolbarsht, Myron L. (1976). "Visual sensitivity of the eye to infrared laser radiation". Journal of the Optical Society of America. 66 (4): 339–341. Bibcode: 1976JOSA...66..339S. doi: 10.1364/JOSA.66.000339. PMID 1262982. The foveal sensitivity to several near-infrared laser wavelengths was measured. It was found that the eye could respond to radiation at wavelengths at least as far as 1,064 nm. A continuous 1,064 nm laser source appeared red, but a 1,060 nm pulsed laser source appeared green, which suggests the presence of second harmonic generation in the retina.

Spectrum and the Color Sensitivity of the Eye" (PDF). Thulescientific.com. Archived (PDF) from the original on 5 July 2010 . Retrieved 29 August 2017.Lynch, David K.; Livingston, William Charles (2001). Color and Light in Nature (2nd ed.). Cambridge: Cambridge University Press. p. 231. ISBN 978-0-521-77504-5. Archived from the original on 8 October 2022 . Retrieved 12 October 2013. Limits of the eye's overall range of sensitivity extends from about 310 to 1,050 nanometers