Fresnel Luminaires Overview
       
Fresnel Optical System

The fresnel (pronounced: 'fren-el') spotlight is easily identified by the stepped surface of the fresnel lens. Fresnel luminaires produce a soft edged beam of light with even light distribution across the beam angle.

The beam angle is adjustable over a wide range, typically from a narrow spot of 6-10 degrees to a flood of 50-60 degrees. This adjustment is achieved by moving the lamp and reflector relative to the lens. An accessory called a barndoor is often fitted to the front of a fresnel luminaire to provide a means of controlling the edges of the beam.

The diagram above shows the basic optical system of a fresnel spot. The fresnel lens is named after its inventor Augustin Fresnel (1788-1827) who developed the lens for use in lighthouses to solve the problems presented by the basic plano-convex lens which was less efficient, too heavy and prone to cracking. The fresnel lens has since become one of the most popular lenses used in luminaires for stage lighting, largely for the same reasons.

Typical Uses

The fresnel spot is a very versatile luminaire that is often used for stage colour washes, as well as for selective highlighting. The soft edge of the beam makes it very easy to blend the beam from one fresnel with the beams of others adjacent to it.
Revised: 21-Dec-2008 Copyright (C) 2005 Adena Limited