Violet light is slowed in a glass of water significantly more than red light.As a result shorter visual waves refract more than do longer ones.They are unified by thinking of them as "electromagnetic waves," waves of alternating strength in electric and magnetic fields that all move through space at the "speed of light" (called "c") of 300,000 kilometers per second (186,000 miles per second), eight times around the Earth in the tick of a clock.
Spectra are commonly seen reproduced either photographically or graphically.
Electromagnetic energy cannot be separated from matter.
The visual spectrum of light, however, is but a tiny portion of the whole picture, of a huge spectrum of radiation that extends in both directions from the edges of the rainbow.
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.
Stand outdoors to see and feel the radiation pouring from the Sun.