Abstract: A lens array for directing infrared light or radiation to a passive infrared detector having at least two Fresnel lenses mounted on or incorporated into the lens array. Each of the lenses has a different infrared detection pattern and the lenses on the array are adapted to be selectively indexed so that the infrared detection pattern of the array is altered by the indexing. The indexing may be accomplished by rotating the lens array or by the linear movement of the lens array.

Abstract: A switch assembly actuated by passive infrared radiation for operating a light in a space, the switch assembly including an optical system which senses infrared radiation over a 180.degree. range in horizontal plane including two separate vertical fields of view, a generally horizontal "look-out" field and a vertical semi cone-shaped "look-down" sensing field for directing to a common sensing element passive infrared radiation produced by a person moving within the sensing field of the switch assembly, the sensing element connected to a control circuit which responsively turns on the light, maintains the light on while the person remains in the space, and turns the light off automatically when the person leaves the space. The switch assembly includes a one-piece optical shell enclosed within a housing which is adapted for installation in a conventional light switch box in room.