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 technically known as parabolic aluminumized reflector or "PAR" lamps. Round PAR lamp diameter is expressed in non-metric units of measurement equal to one eighth 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 200mm wide and 142mm 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.
Read more about Sealed Beam: Automotive Headlamps, Aircraft, Building and Stage Lighting, Lighthouses
Famous quotes containing the words sealed and/or beam:
“These things are not inscribed in tablets, not sealed in the folds of papyri, but you hear them clearly from the tongue in a free mouth.”
—Aeschylus (525–456 B.C.)
“It was at that moment, just after Krug had fallen through the bottom of a confused dream and sat up on the straw with a gasp—and just before his reality, his remembered hideous misfortune could pounce upon him—it was then that I felt a pang of pity for Adam and slid towards him along an inclined beam of pale light—causing instantaneous madness, but at least saving him from the senseless agony of his logical fate.”
—Vladimir Nabokov (1899–1977)