Eventually, halogen sealed-beam lights came to dominate the (U.S.) automotive lamps market.Īircraft landing (ACL) lights are often sealed beams that have a very narrow beam spread. cars in 1979, to enable greater high beam intensity newly permitted by Federal Motor Vehicle Safety Standard 108 without unreasonably high lamp wattage. Halogen sealed-beam headlamps appeared on U.S. With only two round and two rectangular lamp sizes allowed, the sealed-beam headlamp mandate greatly restricted styling possibilities for automobiles. For 1978, a rectangular version of the two-lamp system became legal these measured 200 mm (8 in) wide and 142 mm ( 5 + 1 / 2 in) tall. The new lamps were 165 mm ( 6 + 1 / 2 in) wide and 100 mm (4 in) tall. 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.įrom the 1975 model year, a rectangular version of the four-lamp system was legalized. The following year in 1958, all states allowed the new system. In 1957, a system of four sealed-beam headlamps-two per side, of 5 + 3 / 4 inches (146 mm) diameter, was allowed in some U.S. cars had to have two 7-inch (178 mm) round headlamps with dual filaments, so each lamp provided both a high and a low beam light distribution. Before and after those years, vehicles could have model-specific, nonstandard-shape headlamps, using any of a wide variety of replaceable light bulbs. 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. Two Mercedes-Benz SLs: right with US-spec sealed-beam headlamps left with European-spec composite replaceable-bulb headlamps The focused beam can be oval and is sometimes specified in two numbers. The suffixes given are for 1000-Watt PAR64 lamps only. 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. ĭepending 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. For example, REC142X200 lamps are 142 high and 200 mm wide. 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, a PAR16 lamp is approximately 2 inches or 50.0 mm in diameter. Similarly, the diameter in millimeters can be found by multiplying the PAR designation by 3.125. 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. 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. PAR lamps come in a variety of standardized sizes. 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. The most common sealed beam type combines these three elements into an integral unit. When the lamp burns out or breaks, the whole assembly must be replacedĪ PAR lamp consists of a light source, with lens and a parabolic reflector with a smooth aluminium surface determining the spread of the beam.
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