Because light is a wave, when it passes through a small hole, it is diffracted outwards towards shadow areas. This phenomenon can be used to advantage to control the direction of light by making concentric sawtooth-shaped grooves in the surface of a lens. Such lenses are known as diffractive optical elements. These elements are ideal for the small and light lenses that focus the laser beams used in CD and DVD players. Because the lasers used in electronic devices produce light of a single wavelength, a single-layer diffractive optical element is sufficient to achieve accurate light condensation.