"Spectra" is embedded with links that will take you back to the appropriate parts of the above two sites. The classic colors red, orange, yellow, green, blue, and violet connect in a seemingly infinite number of shades, one blending smoothly into the next.
Together they constitute the "visual spectrum" (or "optical spectrum") because it is the part of the full spectrum that is seen with the human eye.
A single gamma ray photon can carry the energy of over a million million million radio photons.
Light and its partners can be manipulated in a variety of ways.
The smaller the wavelength of the photon the more energy it carries, that is, the greater the ability of the photon to act on some physical substance. You can live near a high-powered radio transmitter with no effect on you and are quite unaware of all the radio photons that constantly surround and pass through you.
Shorter-wave photons have increasingly potent effects. Infrared is felt as heat, visual radiation excites the chemistry of the eye, ultraviolet burns, and no one wants to stand in front of an active X-ray machine for long.
If with superhuman eyes you could see beyond red, you would encounter the "infrared" -- felt as heat on the skin -- which would merge gradually into the familiar "radio" portion of the spectrum.
Spectra are commonly seen reproduced either photographically or graphically.
Electromagnetic energy cannot be separated from matter.
Ultraviolet runs from 4000 A down to about 100 A, X- rays take over to about 1 A, and these are followed by the gamma rays to no known lower limit.
The named divisions are artificial and serve only to block out large spectral segments.