What is Light: Definition and 1000 Discussions

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. A

    I For a relativistic spaceship, what is the most recent news the ship gets from Earth?

    Looking to see if I am in the ballpark correct about this. Let's say a spaceship flies at 99% the speed of light (B=0.99) to a planet 12 light years away. The spaceship is going to land on the planet once it arrives and stay put ever after. Ignore acceleration of start/stop. When it lands on the...
  2. Aryamehr

    I Fluorescent lamps And Fan remote

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  3. SamBiswas95

    If 95% of the atmosphere was SO2, how would the sky look?

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  4. E

    I Can “speed of light” distinguish all Timelapse videos from real motion?

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  5. E

    I Proving speed of light constant “c” is the same in all directions?

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  6. H

    B Are some objects in the night sky just older images of other objects?

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  7. G

    I I want a good reference to a discussion of the meaning of "the speed of light is constant"

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  8. D

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  9. LarryS

    I Planck's Constant times the speed of light

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  10. T

    B Why 186,282?

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  11. dbecker

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  12. felizgu

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  13. H

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  14. K

    A Function to fit the light transmitted from a cavity

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  15. H

    B Do observers always agree on the number of waves in a beam of light?

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  16. G

    I Does the speed of light pop out of other theories than EM?

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  17. M

    B Can objects in nature store light information on the quantum level?

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  18. S

    I Electron counterpart of pseudothermal light source for quantum experiments

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  19. S

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  20. A

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  21. F

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  22. T

    I Light clock running faster than light?

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  23. elou

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  24. Danielk010

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  25. BiGyElLoWhAt

    I Newtonian path of light in a gravitational field

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  26. A

    B Why does light diffraction create circular patterns?

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  27. Hill

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  28. rekha1804

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  29. mister i

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  30. N

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  31. A

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  32. T

    I How does our brain differentiate between a source of light and a painted circle?

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  33. H

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  34. S

    B Redshift of a light pulse between 2 accelerating rockets

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  35. P

    B Is the Speed of Light Consistent Across Rotating Reference Frames?

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  36. Vanadium 50

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  37. S

    B How did expansion take 380,000 years to let light travel freely?

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  38. cathrynliz

    I Can Electrons or Photons Exceed Light Speed?

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  39. L

    I Are photons definitely massless?

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  40. J

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  41. A

    B Gravitrons vs Photons: how come light and gravity exist?

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  42. Pushoam

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  43. CHAIM123

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  44. chemisthypnos

    I Best frequency of radio light to penetrate 1 meter of sea water?

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  45. T

    I Why is there nothing faster than light?

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  46. Aromalsp

    I Constancy of Speed of Light: Postulate or Assumption?

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  47. S

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  48. S

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  49. L

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  50. S

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