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Light is made up of photons...

Why aren't radio waves or gamma radiation made of photons? Aren't they variations of the same thing?

is infra red and ultra violet made of photons? Where is the cut off point?

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  • $\begingroup$ All electromagnetic radiation emerges from a confluence of photons. All . en.wikipedia.org/wiki/Electromagnetic_spectrum . the visible is a tiny part of the range $\endgroup$
    – anna v
    Commented Jan 22, 2017 at 11:53
  • $\begingroup$ Light waves aren't made up of photons. See What is the relation between electromagnetic wave and photon?. However all forms of electromagnetic radiation, radio, infra-red, light, x-ray, etc all exchange energy in photons. $\endgroup$ Commented Jan 22, 2017 at 11:54
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    $\begingroup$ Yes, they are all photons, the difference is the amount of energy involved. Radio frequency photons are harmless to you , UV light photons will give you a tan, whereas gamma rays...you don't want those anywhere near you. $\endgroup$
    – user140606
    Commented Jan 22, 2017 at 11:55

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ALL electromagnetic radiation is tranferred in photons.

From a fundamental physics standpoint, there is nothing that distinguishes light from the rest of the EM spectrum.

Light seems "special" to us as follows: from the standpoint of living, sighted creatures on the surface of a planet near the Sun:

  1. The middle of the visible spectrum is pretty much exactly at the peak of the blackbody spectrum curve for a body with the surface temperature of our Sun. So there's a great deal of this EM radiation around for the purposes of a certain kind of electromagnetic radiation remote sensing we know as "sight";

  2. EM radiation at optical frequencies interact with matter particularly strongly and in striking ways. Optical frequencies are where most metals begin to deviate from perfect conductors (in the sense that the electric field in EM fields of such frequencies intersect metal interfaces at orientations significantly different from the normal), EM radiation of about 1eV is the kind particularly favorable to fluorescence and other wavelength / polarization shifting processes. So EM radiation interacts with the World around sighted living creatures in ways that make it highly useful to probe that World.

In short, these two factors made it pretty much assured from the outset that evolution would come up with creatures that made this particular EM radiation important for sensing the World. Indeed, it is believed sight / eyes have evolved several times, independently of one another, in the animal kingdom.

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All electromagnetic radiation is made of photons, with no exceptions, including radio waves, gamma radiation, infrared, ultraviolet.

(A more precise wording for "made of" is "described quantum mechanically by")

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Visible light is a narrow range of wavelengths (or if you prefer, frequencies) of a much broader spectrum. As seen in this graphic, the human eye can see from red to violet (ROYGBIV = red, orange, green, blue, indigo, violet). Red is around a wavelength of 400 nanometers, violet at around 800 nm. X-rays, UV, and gamma rays have higher frequencies but lower wavelengths; visa versa for IR and microwaves. It helps to think of UV has "extra violet" and IR as "more red".

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