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. The previous design was like that of common flashlights (electric torches), which have a separate small bulb which is fitted in front of a parabolic reflector and covered with a transparent cover, which in the case of a headlamp is ribbed to avoid glare from the filament. This cover would be clamped on with a grommet inbetween to try to seal it; the method's deficiencies were what prompted the sealed beam system. The subsequent design has the reflector sealed to the cover and the small bulb inserted through a hole in the rear of the lamp.
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 became mandatory in the United States in 1940; cars prior to that date could have a variety of shapes of headlamps.