Projection lamps use a built-in reflector to concentrate light in a specific direction. They are used in applications such as overhead projection, semiconductor assembly, medical/scientific instrumentation, and airport runways. They are also used to display movies, microfilm, and slides. Specifications for projection lamps include maximum overall length, light center length, rated average life, lamp power, mean lumens, and color temperature. Typically, maximum overall length is expressed in inches (in). Light center length is the distance between the center of the filament and a reference plane. Lamp labeling rules from the U.S. Federal Trade Commission (FTC) define light output in lumens (lm), a standard unit of measure for the luminous flux or quality of light. Rated average life is the number of burning hours for median life expectancy. Lamp power is the wattage (W) of the lamp. Color temperature measures the visual “warmth” or “coolness” of the light from incandescent lamps. Higher values are associated with lights that are whiter in appearance. 

Lamp Bases and Electrical Connections

Projection lamps use several types of lamp bases and electrical connections. Candelabra bases are designed for decorative lighting applications. Standard candelabra bases include a screw connection. Pre-focus candelabra bases include a pre-focus element, typically a ring. Single-contact candelabras use either a recessed screw contact or a bayonet connection. Medium, medium, bi-post, and medium pre-focus bases are used in standard household lamps up to 300 W and in mercury and sodium lamps under 100 W. Mogul and mogul pre-focus bases are used in mercury, metal halide, and sodium lamps over 300 W. Lamps requiring more than 200 V are likely to use a mogul (or larger) base rather than a medium base. Projection lamps with two or four pin connections are also available. Operating positions for lamp bases are base up, base down, horizontal, and base down to horizontal. 

Selecting Projection Lamps

Selecting projection lamps requires an analysis of filaments, thin strands of wire that are heated electrically to generate radiation in the visible, infrared (IR) and ultraviolet (UV) ranges. Most filaments are made of tungsten, a durable material with great tensile strength that can be heated very near its melting point without evaporating rapidly. Filaments that begin with the letter “C” indicate that the wire was coiled once. Filaments that start with “CC” indicate that the wire was coiled twice. The letters or numbers that follow the “C” or “CC” indicate the position of the filament. C-filament designations include C-2V, C-6, C-6F, C-6 Oval, C-7A, C-8, C-9, C-13, and C-13D. CC-filament designations include CC-2V, CC-6, CC-8, and 2CC-8. Other filament configurations for projection lamps include BP, FF, M, MP, and SC.