A parabolic aluminized reflector lamp (PAR lamp or simply PAR) is a type of electric lamp that is widely used in commercial, residential, and transportation illumination. It produces a highly directional beam. Usage includes theatrical lighting, locomotive headlamps, aircraft landing lights, and residential and commercial recessed lights ("cans" in the United States).
Many PAR lamps are of the sealed beam variety, with a parabolic reflector, one or more filaments, and a glass or plastic lens sealed permanently together as a unit. Originally introduced for road vehicle headlamp service, sealed beams have since been applied elsewhere. Halogen sealed beam lamps incorporate a halogen lamp within a quartz or hard glass envelope.
Construction
A PAR lamp consists of a light source, with lens and a parabolic reflector with a smooth aluminium surface determining the spread of the beam. The most common sealed beam type combines these three elements into an integral unit. The light source usually approximates a point source that can be focused on; tungsten filaments and halogen lamps are common, but some theatrical usage that requires a higher color temperature may use hydrargyrum medium-arc iodide (HMI) instead.
Sizes
PAR lamps come in a variety of standardized sizes. The size of a round PAR lamp is expressed as the nominal diameter of the mouth of the reflector, in eighths of an inch—so the approximate nominal lamp bell diameter in inches can be found by dividing the PAR size by 8. A PAR56, for example, is 56 eighths of an inch (7 inches) in diameter; a PAR36 is 36 eighths (4.5 inches) in diameter, and so on. Similarly, the diameter in millimeters can be found by multiplying the PAR designation by 3.175. For example, a PAR16 lamp is approximately 2 inches or 50.8 mm in diameter.
The size of rectangular PAR lamps is expressed as the letters REC followed by the reflector's mouth height, the letter "X", and the reflector's mouth width—with both dimensions in millimeters. For example, REC142X200 lamps are 142 high and 200 mm wide.
Light beams
Depending on the parabolic reflector geometry, the configuration of the filament and its placement within the paraboloid, PAR lamps can achieve a wide range of beams, from narrow spot to wide flood. The following suffixes are commonly used with PAR lamps to indicate their beam width: PAR lamps are also manufactured to produce beam patterns specific to the needs of particular applications, such as low beam and/or high beam headlights and fog and driving lights for vehicles, and warning lamps for school buses.
The suffixes given are for 1000-Watt PAR64 lamps only. The focused beam can be oval and is sometimes specified in two numbers.
Uses
Automotive headlamps
In the United States of America, sealed-beam headlamps were introduced in 1939, becoming standard equipment across all American-market vehicles starting in 1940 and remaining the only type allowed for almost four and a half decades, until the 1984 model year. Before and after those years, vehicles could have model-specific, nonstandard-shape headlamps, using any of a wide variety of replaceable light bulbs. Between 1940 and 1956, all U.S. cars had to have two round headlamps with dual filaments, so each lamp provided both a high and a low beam light distribution. In 1957, a system of four sealed-beam headlamps—two per side, of diameter, was allowed in some U.S. states. The following year in 1958, all states allowed the new system. Two of the lamps contained two filaments and served as low and high beam, while the other two lamps contained only one filament and were active only during high-beam operation.
From the 1975 model year, a rectangular version of the four-lamp system was legalized. The new lamps were wide and tall. For 1978, a rectangular version of the two-lamp system became legal; these measured wide and tall.
With only two round and two rectangular lamp sizes allowed, the sealed-beam headlamp mandate greatly restricted styling possibilities for automobiles.
Halogen sealed-beam headlamps appeared on U.S. cars in 1979, to enable greater high beam intensity newly permitted by Federal Motor Vehicle Safety Standard 108 without unreasonably high lamp wattage. Eventually, halogen sealed-beam lights came to dominate the (U.S.) automotive lamps market.
Aircraft
Aircraft landing (ACL) lights are often sealed beams that have a very narrow beam spread. They typically have a size of PAR36 or PAR64, and run on 28 V DC. They have found some use in stage lighting as well.