Headlights are mounted on the front of the car to light the road ahead during night or foggy days. They have reflectors and special lenses and are usually the sealed beam construction type, with the filament, reflector and lens fused together into an airtight unit. The most popular type of headlight is the halogen type, because it provides bright illumination. The halogen bulb is filled with pressurized gas (halogen) and can produce flying fragments if shattered. Wear protective glasses for changing a halogen lamp and always throw out the old one in the protective carton that comes with the new one.
Types of headlights
A light source (filament or arc) is placed at or near the focus of a reflector, which may be parabolic or of non-parabolic complex shape. Fresnel and prism optics moulded into the headlight lens then shift parts of the light laterally and vertically to provide the required light distribution pattern. The lens may use both refraction and TIR to archive the desired results. Most sealed-beam headlights have lens optics.
optics required to give the proper light distribution pattern is designed into the reflector itself, with such a unit being known as an “optic reflector”. The reflector design starts as a parabola standing in for the size and shape of the completed package. The optical engineer replaces the entire surface with individual segments of specifically calculated, complex contours. The precise shape of each segment is designed such that their cumulative effect produces the required distribution pattern.
Optic reflectors are commonly made of compression-moulded or injection molded plastic, though glass and metal optic reflectors also exist. The reflective surface is vapor deposited aluminum with a clear overcoating to prevent the extremely thin aluminum from oxidizing. Extremely tight tolerances must be adhered to in the design, tooling and production of complex-reflector headlamps.
In this system a filament is located at one focus of an elliptical reflector and has a condenser lens at the front of the lamp. A shade is located at the image plane, between the reflector and lens, and the projection of the top edge of this shade provides the low-beam cutoff. The shape of the shade edge, and its exact position in the optical system, determines the shape and sharpness of the cutoff. The shade may have a solenoid actuated pivot to provide both low and high beam, or it may be stationary in which case separate high-beam lamps are required. The condenser lens may have slight fresnels or other surface treatments to reduce cutoff sharpness. Recent condenser lenses incorporate optical features specifically designed to direct some light upward towards the locations of retroreflective overhead road signs.