The horizontal distance between crests is referred to as a wavelength. The electromagnetic spectrum is the full range of all the represented wavelengths. The electromagnetic spectrum As you can see from above, the range of visible light is between 380 and 750 nm. This is where we get the colors we perceive. When the energy of visible light is absorbed by matter, it can be measured in photons.
Pigments are different molecules which absorb wavelengths of light.
Most pigments absorb only some wavelengths and transmit the rest. One way to show how effective a pigment molecule absorbs different light wavelengths is by using the absorption spectra. The two spectra shown below indicate how efficiently chlorophyll a and b respond to wavelengths. Each pigment has a light-catching array of atoms, which are often joined by alternating single and double bonds. In a pigment molecule, an input of energy destabilizes the electron distribution in the light-catching array.