Wavelength of light determines the nature of the light. We can describe light as electromagnetic waves with color identified by its wavelength. A single photon of one color differs from a photon of another color only by its energy. Visible light is the range of wavelengths within the electromagnetic spectrum that the eye responds. Red light has a different wavelength to that of blue light and green light has a different wavelength from both of them.


Intensity is like brightness, and is measured as the rate at which light energy is delivered to a unit of surface, or energy per unit time per unit area. Different wavelengths of light also have more or less energy, depending on whether the wavelength is shorter or longer. So the energy of light depends on both intensity and wavelength.

In the diagram below there are two waves both of the same wavelength but with different amplitudes. The amplitude of a wave tells us about the intensity or brightness of the light relative to other light waves of the same wavelength. Both Wave 1 and Wave 2 have the same wavelength but different amplitudes.

Object Color

Color is produced by the absorption of selected wavelengths of light by an object. Objects can be thought of as absorbing all colors except the colors of their appearance which are reflected. A blue object illuminated by white light absorbs most of the wavelengths except those corresponding to blue light. These blue wavelengths are reflected by the object.