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A sealed beam is a type of unitized lamp with a parabolic reflector, one or more filaments, and a glass or polycarbonate lens all permanently attached together and sealed. Originally introduced for road vehicle headlamp service, sealed beams have since been applied elsewhere. Halogen sealed beam lamps have an inbuilt halogen lamp with the filaments contained in a quartz or hard glass envelope. Sealed beams are parabolic aluminized reflector or "PAR" lamps. Round PAR lamp diameter is expressed in eighths of an inch, so a PAR56 lamp, for example, is 56/8" (i.e., 7 inches) in diameter. Other popular sizes are PAR30, PAR36, PAR38, PAR46, and PAR64. Rectangular PAR lamp size is expressed in millimeters, so a PAR200×142 is 200 mm wide and 142 mm tall. Sealed beams are available in a variety of nominal voltage ratings, most commonly 6, 12, 24, 28, 120, and 230 V. The actual operating voltage may differ from the nominal rated voltage; for example, "12 volt" sealed beam headlamps are meant for use in automobiles with typical line voltage of 13.5 to 14.2 with the engine running. ==Automotive headlamps== (詳細はFederal Motor Vehicle Safety Standard 108, which at the time required all headlamps to be of sealed beam construction; eventually halogen sealed beams came to dominate the sealed beam lamp market. The limited range of standardized sealed beam headlamp sizes and shapes restricted styling options for automobiles. Replaceable-bulb headlamps provide the regulated light distributions while allowing greater design and engineering freedom.〔Horst Bauer ''Bosch Automotive Handbook 4th Edition'' Robert Bosch GmbH, Stuttgart 1996 ISBN 0-8376-0333-1 page 710〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「sealed beam」の詳細全文を読む スポンサード リンク
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