A sealed beam is a type of lamp that includes a reflector and filament as a single assembly, over which a front cover (lens), usually of clear glass, is permanently attached.Sealed beams come in various voltages, most commonly 6, 12, 28, and 120 V. Aircraft landing lights, which are commonly used in the open-air, concerts and 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.Headlights for automobiles may be of the sealed beam type. It means that the reflectors array on the front and the bulbs are a unit and must be replaced together in case of burnt out.In theatrical lighting, sealed beam type fixtures are often used. A common size, which used in rock concerts, as well as outdoor architectural lighting, is the Parabolic Aluminum Reflector 64 (PAR64). The PAR is a non-SI unit of measure equal to one eighth of an inch, so a PAR64 light is a light which 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.