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A burnt-out sealed beam, broken open to show internals. When the lamp burns out the whole assembly (reflector, lamp, lens array) must be replaced. The advantage is very good alignment, and being completely impervious to dirt, moisture, etc.

A sealed beam is a type of lamp that includes a reflector and filament as a single assembly, over which a front cover (lens) of clear glass, is permanently attached. Previously, automotive headlamps used a separate small bulb and reflector covered with a ribbed lens to avoid glare from the filament. This cover would be clamped on with a grommet to seal it. The method's deficiencies prompted the invention of the sealed beam system.

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Automotive headlamps

Headlights for automobiles may be of the sealed beam type, meaning that the reflector, the lens array on the front and the bulb are all one unit that must be replaced together in case of burnout. They are clamped into a structure for aiming the beams to meet safety requirements. Every time the headlight is replaced, the aiming of the beams must be checked. Headlights using sealed beams were introduced in the United States in 1940 and became mandatory from the following year until the 1984 model year; cars prior and subsequent to that date could have a variety of shapes of headlamps. The limited range of standard sealed-beam lamps restricted styling options for automobiles, and current headlamp designs allow mandated light levels to be obtained with more compact lamps. [1]

Sealed beams come in various voltages, most commonly 6, 12, 28, 120 and 230 V. Aircraft landing lights, which are also used in open air concerts and for stage lighting, are sealed beams that have a very narrow beam spread.

Modern sealed beams have an additional envelope around the filament, whereas older types do not. The inner envelope contains a halogen to improve the life of the filament and enable more light for the same power; for this to work, the halogen must be confined to the area around the filament by the second envelope, commonly made of fused quartz to withstand the filament's heat. These "halogen sealed beams" appeared on U.S. cars in 1978 to enable halogen technology under Federal Motor Vehicle Safety Standard 108, which at the time required sealed beam headlamps; they continued even after FMVSS 108 was amended to permit composite headlamps in 1983, and came to dominate the sealed beam lamp market.

Building and stage lighting

In stage lighting, sealed beam lamps are often used. A common size, also used in rock concerts, as well as outdoor architectural lighting, is the parabolic aluminumized reflector 64 (PAR64). PAR lamps are measured in non-SI units of measurement equal to one eighth of an inch, so a PAR64 light is a light that is 8 inches in diameter. The fixtures that such sealed beam lights go into are called "PAR cans", so a PAR64 fixture is an 8 inch diameter can.

Other popular sizes are PAR56, PAR38, and PAR36.

Beam spreads are designated as FL (flood), SP (spot), NSP (narrow spot), and VNSP (very narrow spot), as stamped on the back of the lamp's reflector.

A PAR64 sealed beam typically comes in 250 W, 500 W, or 1000 watt.

See also

References

  1. ^ Horst Bauer Bosch Automotive Handbook 4th Edition Robert Bosch GmbH, Stuttgart 1996 ISBN 0-8376-0333-1 page 710
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