The human eye responds to a narrow band of energy in the electromagnetic spectrum called the visible light spectrum. The visible spectrum ranges from deep violet (~ 390 nm) to deep red (~ 750nm). Human eyes cannot distinguish individual wavelengths but can discriminate multiple colors and shades.
The electromagnetic spectrum can be described as an infinite number of slices. Each slice is a wavelength. The wavelength tells something about its energy. The energy contained in visible light is just as real as the energy of other wavelengths that are employed for common uses. Radio and TV, Microwave ovens, germicidal and heating lamps are common devices that exploit specific portions of the electromagnetic spectrum.
Lower wavelength light in the violet region is more energetic than longer wavelength light in the red region. The color of a wavelength smoothly changes from one slice to the next.