The exploitation of "light", the electromagnetic spectrum, is accomplished with common objects and materials which control and direct the electromagnetic fields. For example, a glass lens in a camera is used to produce an image, a metal cage may be used to screen sensitive equipment, and radio antennas are designed to transmit and receive daily FM broadcasts. Homogeneous materials, which manipulate or modulate electromagnetic radiation, such as glass lenses, are limited in the upper limit of refinements to correct for aberrations. Combinations of inhomogeneous lens materials are able to employ gradient refractive indices, but the ranges tend to be limited.