Light Definition and 1000 Threads

Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), 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 primary properties of visible light are intensity, propagation-direction, frequency or wavelength spectrum and polarization. Its speed in a vacuum, 299 792 458 metres a second (m/s), is one of the fundamental constants of nature, as with all types of electromagnetic radiation (EMR), light is found in experimental conditions 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 electromagnetic 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.
The main source of light on Earth is the Sun. 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.

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  1. K

    I Will anti-parallel light beams between two stars stay parallel?

    In our galaxy, two stars, A and B, move about 20 km/s in slightly different directions to each other. The stars are about 15 light years apart. Initially, the light beams are exactly anti-parallel. Will light beams emitted from star A traveling towards light beams emitted from star B stay...
  2. M

    I Rare Kaon decay may shed light on new physics....maybe

    The phys.org summary had me intrigued and the resulting new paper makes for heavy reading at my level of knowledge, but it was the underlying reasoning of the methodology that I really question: One of the authors notes "It's so rare, that they should not have seen any." From that, the...
  3. TaurusSteve

    Stargazing Convert Light Years to Miles: 5.879e+12 Explanation and Conversion Guide

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  4. K

    Polarization of light -- Determine the thickness of the crystal

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  5. LawH

    B Energy, Mass, Speed of Light: Can We Reach It?

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  6. L

    Faster than light thought experiment

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  7. skyshrimp

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  8. R

    B Meaning of "Speed of Light is Constant": Explained

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  9. R

    B Constant speed between 2 objects close to the speed of light

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  10. R

    B Moving Faster Than Light: Are There Symmetrical Rules?

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  11. A

    I Why is the speed of light absolute?

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  12. H

    B If space is transparent how can we not view light from a black hole

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  13. B

    I Everyone Measures Light in a Vacuum at the Same Speed

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  14. H

    I Measuring the Speed of Light: How Did We Do It?

    I understand that the meter is defined from the speed of light (distance light travels in 1/299792458 of a second). But how did man measure this exact distance to this level of precision? With any apparatus, isn't there an unknown amount of bottleneck somewhere?
  15. angela6884

    Misc. How can I enlarge the light produced by a laser?

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  16. C

    I One Way Speed of Light: Is it Constant?

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  17. R

    A doubt on Electrostatics -- An electrified rod attracting light objects

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  18. E

    Young's experiment - lowering the light intensity of one slit

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  19. S

    I How to calculate the wavelength of light coming from 1 light year away

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  20. E

    Drop in intensity when light is focused to a point (telescope mirror)

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  21. J

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  22. jisbon

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  23. J

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  24. A

    I Is the energy of a burst of light the sum of the energy of each photon?

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  25. F

    Laser light vs "Regular" Light

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  26. Uchida

    I Minimum number of cycles in a short pulse laser

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  27. Adesh

    Derivation of [itex] p = \frac{E}{c} [/itex] using Maxwell's light

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  28. G

    I Speed of Light: Measuring Meters and Seconds

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  29. J

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  30. K

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  31. Z

    I Information in a light beam relative to the width of the beam?

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  32. dom489

    How can I increase the wavelength of light photons?

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  33. S

    How can light hit one part of a ganglion cell but not another part?

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  34. J

    The electromagnetic nature of light

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  35. J

    Electrical Automotive Alternator with External Regulator Light stays on all the time

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  36. F

    How does polarization show the wave nature of light?

    I'm a high school teacher. In the curriculum, students are required to explain that polarization of light shows that light is a transverse wave. My answer: In order to explain polarization, we have to consider the electric field vibration direction. For example, on a wave that propagates...
  37. sigr

    B What Would Light Look Like If Train Moved at > Speed of Light?

    I am reading up on the special theory of relativity, and watched a video. In the video we have a train moving at ½ c towards a station, where an observer is waiting. The train's headlamp is on. How would the lamp's light appear to the observer? I was thinking that it¨'d appear to the observer...
  38. peace

    Elliptically polarized light & partially-polarized light

    How to distinguish elliptical polarized light from partially-polarized light?
  39. C

    Incandescent light lamp flickering is due to what?

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  40. nightvidcole

    Is Visible Light Bremsstrahlung Observable in Transparent Mediums?

    Summary: Can one observe visible light bremsstrahlung when an electron beam stops in a transparent medium? The theoretical form of a bremsstrahlung spectrum is flat at low photon energies. This means that even a high energy electron beam incident on matter should cause the emission of visible...
  41. S

    B We see a quasar 13 billion light years away. What does this mean?

    Summary: If the furthest quasars we can see are let's say 13 billion light years away from us, then does this mean that the distance between us and that quasar was 13 billion light years at 13 billion years ago? To anyone educated in physics this might be a silly question but to me this is...
  42. N

    Can I read a book with an infrared led light?

    I am not a physics guy I'm just a husband trying to read in bed at night without disturbing my wife. Does infrared light reading glasses exist?Scientificly, can they be made?
  43. M

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  44. mastermechanic

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  45. A

    Density Matrix of Unpolarized Light

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  46. A

    The Nuclear Rocket that Could Reach 20% of the Speed of Light

    In 2009, the same society together with the Tau Zero Foundation announced Project Icarus, a similar spacecraft that could achieve 15% the speed of light. That year, a physicist called Friedwardt Winterberg announced a fusion spacecraft that could be used as a capacitor to produce proton...
  47. R

    B Can photons of visible light lose energy and become sub-visible?

    Let me clarify this by a thought experiment: Imagine, a heated, red-hot (emitting only monochromatic red light) metal bar is brought inside a dark room. The room is practically insulated and the metal bar is glowing in the dark - emitting 'red photons' of visible light. Eventually, the bar...
  48. K

    Making a custom DIY light switch safe for home use

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  49. N

    Scattering of Light in Different Media

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  50. Addez123

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