Lenses work by refraction: light changes direction when it strikes the surface. By curving the lens profile away from the light source, this refraction can be used to ensure all light leaves the lens in the same direction. The optical principle of the Fresnel was invented by the French physicist Augustin Jean Fresnel as a way of reducing the huge bulk and weight required for large lighthouse lenses. By splitting the lens profile into sections, the curved profile can effectively be made in the form of a flat sheet.
Using this principle in optical rear projection screens, it is possible to control projected light so that it exits the lens perpendicular to the screen – although the light has entered in a conical pattern. The Fresnel lens on an optical rear projection screen consists of thousands of concentric lens element rings, each having a different and specific angle with which to bend the light.
The Fresnel element generates two key benefits:
But the Fresnel is useless by itself! Further techniques and technologies are required to deliver the projected light to viewers. Often this technology is in the form of lenticular lenses.