Parts of a Headlight Assembly – Labeled Car Headlight

All 12 parts on the diagram

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Pulled apart, front to back 8

Lens On a headlight like this it only protects what is behind it. The reflector shapes the beam. Modern lenses are hard-coated plastic.
Housing (headlight body) The lens closes its front. The bulbs go in through holes in its back. It bolts to the car.
Reflector The bulb's filament sits at the focus of the bowl. The bowl throws its light forward as a beam.
Low-beam bulb The low beam is aimed down at the road. That way it does not dazzle other drivers. The bulb is held by its base. The glass is not touched.
Filament It gives off the light when current heats it. It is the light source the reflector is built round.
Bulb retaining spring It holds the bulb's flange in its hole. It is unclipped and swung aside to change the bulb. Some makers call it the hold-down wire.
Rubber cover (weather seal) It seals the back of the housing round the bulb. It has to fit snugly on the headlight body.
Connector It pushes onto the prongs of the bulb. It goes through the hole in the rubber cover.

The back of the housing 4

High-beam bulb The high beam lights the road farther ahead. It is switched to low beam when another vehicle is near.
Turn signal bulb It flashes to show a turn. It pulls straight out of its socket.
Socket A quarter turn unlocks it from the housing. It comes out with the bulb in it.
Aiming screws Turning them tilts the light to aim the beam. One car maker's manual calls them adjustment bolts.

How this list was compiled: Part names checked on 2026-09-30; a name is kept only when two independent sources use it. (1) Wikipedia, Headlamp, text only (lens and cover lens, reflector, filament, bulb, low beam and high beam, housing, polycarbonate lenses, turn signal). (2) US Army TM 9-8000, Principles of Automotive Vehicles, 1985, paragraph 16-4, https://archive.org/details/tm-9-8000-principles-of-automotive-vehicles-1985 (lens, reflector, filament at the focal point, mounting socket, aiming screw, upper and depressed beams). (3) A 1998 sedan owner's manual, section on replacing light bulbs, and a 2005 sedan owner's manual from the same maker (connector, rubber cover, bulb retaining spring, bulb, headlight body, low and high beam, front turn signal light, headlight aim adjustment bolts); the two count as one source. (4) A 2007 pickup owner's manual from another maker (halogen headlight bulb handled by its base, electrical connector, rubber weather seal, hold-down wire, headlight assembly, socket turned a quarter turn, bulb pulled straight out, high and low beam, turn signal). The owner's manuals were read as plain text copies held by this project. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; no maker's lamp, nothing traced. Licence: own work

How it works

The parts of a headlight fit in one housing: a lens in front, a reflector behind it, and bulbs that go in from the back. The second view is what you see under the hood.

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Front to back, then round the back

The first view spreads the assembly out in the order it goes together: lens, housing with its reflector, bulb, retaining spring, rubber cover and connector. The housing is drawn cut open so the reflector shows. The second view is the back of the same housing: one bulb with its cover on, one with it off, the turn signal bulb pulled out in its socket, and the two aiming screws.

A headlight bulb is handled by its base. Oil from a finger on the glass can make it overheat.
This is a reflector headlight with halogen bulbs. Projector and LED headlights are built differently.

Questions and answers

What are the parts of a headlight assembly?

A housing with a clear lens on the front and a reflector inside; a low-beam and a high-beam bulb, each held by a retaining spring and sealed by a rubber cover; a connector for each; a turn signal bulb in its socket; and aiming screws.

What is the clear front of a headlight called?

The lens. On older headlights the lens has flutes and prisms that spread the light. On most modern ones it is a clear cover that only protects the inside, and the reflector shapes the beam.

What is the difference between the low beam and the high beam?

The low beam points down at the road so it does not dazzle drivers coming the other way. The high beam lights the road much farther ahead and is for when no other vehicle is near.

What holds a headlight bulb in place?

On this kind of headlight, a retaining spring: a wire clip swung over the bulb's flange. A rubber cover then seals the back, and the connector plugs onto the bulb.