An Overview Of Headlight Types
Headlights allow drivers to safely navigate their vehicles in the dark or in low-visibility circumstances. Since their invention in the late 1880′s, the standard automotive headlight has gone through several changes. Technology continues to develop lamps that are bigger, better, and brighter than ever before.
Headlamp Technologies
In the beginning, headlights were constructed with tungsten filaments identical to those found in a standard incandescent bulb.
Soon after the development of the tungsten bulb, halogen technology arrived. While halogen bulbs still used the same tungsten filament, the addition of a halogen vapor such as bromine or iodine allowed the devices to produce more light at the same energy input. Alternatively, halogens can produce the same amount of light at less power resulting in improved efficiency. Halogen bulbs produce a soft white light, unlike the harsh blue found in HID lamps.
HID lamps, otherwise known as high-intensity discharge lamps, are the latest advancement in headlamp technology. Lacking a filament, these bulbs operate by passing current through a vapor-filled bulb. The most common chemical used is xenon, noted for its harsh, distinctive blue light. Compared to halogen and tungsten-filament bulbs, HID lamps are far more powerful.
Optical Systems
The two main headlamp varieties are reflector lamps and projector lamps. With reflector lamps, the light source is placed at the focus of a reflector (either parabolic or non-parabolic), from which the light bounces off and travels through a lens. The lens is molded with prism and Fresnel optics for optimum delivery.
Projector lamps use a condenser lens in order to intensify the beam of light. The bulb is placed in the focus of an ellipsoidal reflector, and the light produced reflects off and is concentrated at the lens. A shade is placed between the lens and reflector in order to modify the beam and in some cases, switch between high and low beam settings.
Low And High Beam Usage
Regardless of the light source or optical system, headlight use is broken up into two modes: high and low beam. With low beams, the light is directed downward to prevent glare from impacting other motorists. Pointed down, they can illuminate the road surface several feet in front of a vehicle. With high beams, a secondary set of lamps is activated, producing light that is uncontrolled and directed forward. High beams are powerful enough to blind other drivers, and should only be used when there are no cars on the road in front of you.
In addition to high and low beam settings, many modern cars are now coming equipped with DRL or daytime running lights. Daytime running lights operate on reduced voltage and are intended to increase driver visibility. That said, in the constant pursuit of improved driver safety, manufacturers continue to develop new headlight solutions for tomorrow’s vehicles.