EMR in the visible light region consists of quanta (called photons) that are at the lower end of the energies that are capable of causing electronic excitation within molecules, which leads to changes in the bonding or chemistry of the molecule. At the lower end of the visible light spectrum, EMR becomes invisible to humans (infrared) because its photons no longer have enough individual energy to cause a lasting molecular change (a change in conformation) in the visual molecule retinal in the human retina, which change triggers the sensation of vision. Different physicists have attempted to measure the speed of light throughout history. Galileo attempted to measure the speed of light in the seventeenth century. An early experiment to measure the speed of light was conducted by Ole Rømer, a Danish physicist, in 1676. Using a telescope, Rømer observed the motions of Jupiter and one of its moons, Io. Noting discrepancies in the apparent period of Io's orbit, he calculated that light takes about 22 minutes to traverse the diameter of Earth's orbit. [15] However, its size was not known at that time. If Rømer had known the diameter of the Earth's orbit, he would have calculated a speed of 227 000 000 m/s.

The other main properties of light are intensity, polarization, phase and orbital angular momentum. When the concept of light is intended to include very-high-energy photons (gamma rays), additional generation mechanisms include:

Solar Sails Could Send Spacecraft 'Sailing' Through Space". NASA. 31 August 2004. Archived from the original on 21 October 2012 . Retrieved 30 May 2008. 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. where θ 1 is the angle between the ray and the surface normal in the first medium, θ 2 is the angle between the ray and the surface normal in the second medium and n 1 and n 2 are the indices of refraction, n = 1 in a vacuum and n> 1 in a transparent substance. Narinder Kumar (2008). Comprehensive Physics XII. Laxmi Publications. p. 1416. ISBN 978-81-7008-592-8. Main article: Refraction Due to refraction, the straw dipped in water appears bent and the ruler scale compressed when viewed from a shallow angle.

Hignett, Katherine (16 February 2018). "Physics Creates New Form of Light That Could Drive The Quantum Computing Revolution". Newsweek. Archived from the original on 25 April 2021 . Retrieved 17 February 2018. In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. [2] [3] This article is about visible light. Read the electromagnetic radiation article for the general concept.The photometry units are different from most systems of physical units in that they take into account how the human eye responds to light. The cone cells in the human eye are of three types which respond differently across the visible spectrum and the cumulative response peaks at a wavelength of around 555 nm. Therefore, two sources of light which produce the same intensity (W/m 2) of visible light do not necessarily appear equally bright. The photometry units are designed to take this into account and therefore are a better representation of how "bright" a light appears to be than raw intensity. They relate to raw power by a quantity called luminous efficacy and are used for purposes like determining how to best achieve sufficient illumination for various tasks in indoor and outdoor settings. The illumination measured by a photocell sensor does not necessarily correspond to what is perceived by the human eye and without filters which may be costly, photocells and charge-coupled devices (CCD) tend to respond to some infrared, ultraviolet or both. 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

Buser, Pierre A.; Imbert, Michel (1992). Vision. MIT Press. p. 50. ISBN 978-0-262-02336-8 . Retrieved 11 October 2013. Light is a special class of radiant energy embracing wavelengths between 400 and 700 nm (or mμ), or 4000 to 7000 Å. White light is made up of all the different colors of light added together. When white light shines through a prism, it splits up into different colors, becoming a spectrum. The spectrum contains all of the wavelengths of light that we can see. Red light has the longest wavelength, and violet (purple) light has the shortest. 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. Ohannesian, Lena; Streeter, Anthony (2001). Handbook of Pharmaceutical Analysis. CRC Press. p. 187. ISBN 978-0-8247-4194-5 . Retrieved 20 October 2013.

Light sources

The fact that light could be polarized was for the first time qualitatively explained by Newton using the particle theory. Étienne-Louis Malus in 1810 created a mathematical particle theory of polarization. Jean-Baptiste Biot in 1812 showed that this theory explained all known phenomena of light polarization. At that time the polarization was considered as the proof of the particle theory.

The wave theory predicted that light waves could interfere with each other like sound waves (as noted around 1800 by Thomas Young). Young showed by means of a diffraction experiment that light behaved as waves. He also proposed that different colours were caused by different wavelengths of light and explained colour vision in terms of three-coloured receptors in the eye. Another supporter of the wave theory was Leonhard Euler. He argued in Nova theoria lucis et colorum (1746) that diffraction could more easily be explained by a wave theory. In 1816 André-Marie Ampère gave Augustin-Jean Fresnel an idea that the polarization of light can be explained by the wave theory if light were a transverse wave. [37] Light or visible light is electromagnetic radiation that can be perceived by the human eye. [1] Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 terahertz, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths). [2] [3] A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (green-blue) are separated. Above the range of visible light, ultraviolet light becomes invisible to humans, mostly because it is absorbed by the cornea below 360 nm and the internal lens below 400 nm. Furthermore, the rods and cones located in the retina of the human eye cannot detect the very short (below 360 nm) ultraviolet wavelengths and are in fact damaged by ultraviolet. Many animals with eyes that do not require lenses (such as insects and shrimp) are able to detect ultraviolet, by quantum photon-absorption mechanisms, in much the same chemical way that humans detect visible light. When light is refracted in raindrops, a rainbow is made. The raindrop acts like a prism and refracts the light until we can see the colors of the spectrum. Rainbow in Budapest shows the colors of the visible spectrum. Color changeAntognozzi, M.; Bermingham, C. R.; Harniman, R. L.; Simpson, S.; Senior, J.; Hayward, R.; Hoerber, H.; Dennis, M. R.; Bekshaev, A. Y. (August 2016). "Direct measurements of the extraordinary optical momentum and transverse spin-dependent force using a nano-cantilever". Nature Physics. 12 (8): 731–735. arXiv: 1506.04248. Bibcode: 2016NatPh..12..731A. doi: 10.1038/nphys3732. ISSN 1745-2473. S2CID 52226942. 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. Berns, Roy S. (2019). Billmeyer and Saltzman's Principles of Color Technology. Fred W. Billmeyer, Max Saltzman (4th ed.). Hoboken, NJ: Wiley. ISBN 978-1-119-36668-3. OCLC 1080250734.