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:
““Our snowstorms as a rule
Aren’t looked on as man-killers, and although
I’d rather be the beast that sleeps the sleep
Under it all, his door sealed up and lost,
Than the man fighting it to keep above it,
Yet think of the small birds at roost and not
In nests....””
—Robert Frost (1874–1963)
“What do we plant when we plant the tree?
We plant the ship that will cross the sea,
We plant the mast to carry the sails,
We plant the planks to withstand the gales—
The keel, the keelson, and beam and knee—
We plant the ship when we plant the tree.”
—Henry Abbey (1842–1911)