Visible light is only part of the electromagnetic spectrum, which also includes ultraviolet light, infrared, radios, X-rays and microwaves. The electromagnetic spectrum is a description of energy that is radiated from its source.

Energy Levels

Radio waves, with long wavelengths and low energy and frequencies, are at the bottom of the spectrum. As the spectrum moves from radio to microwave to infrared to visible light to ultraviolet to X-rays and finally to gamma rays, the wavelengths get shorter and both the energy and frequencies get higher.

Visible Spectrum

The portion of the electromagnetic spectrum that contains visible light and is emitted by such sources as light bulbs and stars is called the optical spectrum. It contains all the different colors, which are determined by their wavelength.

Color

The human eye perceives light emitted from the sun as white light, meaning that it contains all the colors of the spectrum. Colors range in wavelengths from 400 nanometers for violet to 700 nanometers for red.

Absorption

Because blue light scatters more easily by the earth's atmosphere, the sky appears blue to observers. Plants absorb all color of light except green, which they reflect back out, giving plants the appearance of being green. Sunsets and sunrises sometimes appear red because the longer wavelengths have not been removed by the atmosphere.

Infrared and Ultraviolet

Infrared and ultraviolet light are the parts of the electromagnetic spectrum at either end of the visible spectrum, not being visible to human observation. Infrared has longer wavelengths than visible light, while ultraviolet is shorter and has a higher frequency.

Source:

NASA: Electromagnetic Spectrum

Atmospheric Science Data Center: What Wavelenghth Goes with a Color

Michigan State University: Visible and Ultraviolet Spetroscopy