Headlights: Illuminating the Darkness

It’s easy to take headlights for granted, but their importance is almost impossible to overstate. Of all the different automobile components that have developed over the years, headlights are one of the single most important. From humble gas lamps to adaptive technologies that allow you to peer around corners, headlights have been helping to illuminate the darkness since the very first days of the automobile.



Headlights have been helping to illuminate the darkness almost since day one.

History of Headlights

Although headlights weren’t standard equipment on many of the first automobiles, although they have been since 1904. Since then, the headlight has gone through an almost constant technological evolution, which has been driven in part by the relative danger of driving during the night versus driving during the day. According to the NHTSA, about half of all automobile-related fatalities happen during the nighttime hours even though over three quarters of all traffic occurs during the daytime hours.

acetylene headlights

Acetylene headlights were popular prior to the widespread adoption of electric headlights since they performed well in the rain.

Since early automobiles lacked electrical systems, the first headlamps were actually that — gas lamps. These early headlights burned oil and other fuels, and they didn’t operate too well in inclement weather, which is when headlights are needed the most. For that reason, acetylene lamps that worked well in the rain became popular. Electric headlights were also first offered in 1898, although problems with filament life and electricity production limited their popularity.

The first standard equipment headlights appeared in 1904 in the form of of the “prest-o-lite” acetylene headlamp. These gas lamps continued to dominate the automotive industry until Cadillac started using their electrical ignition systems to power electric headlights. Coincidentally, this also proved to be the genesis of the modern automotive electrical system.

autronic eye automatic headlights

GM’s “autronic eye” was an early example of automatic headlights.

Headlight technology progressed at a rapid pace, with low and high beams being introduced in 1917 and foot-operated dimmer switches appearing in 1927. These foot-operated switches persisted almost until the present day, with the last one appearing right around the 1991 model year. Automatic high and low beams also showed up pretty early on with the “autronic eye” that was available from Cadillac for the 1954 model year, and adaptive headlights were experimented with even earlier on with Tatra’s steering-linked third “cornering” headlight. (Although adaptive headlights rapidly fell out of favor until their reintroduction in recent years.)

Sealed beam headlights were first introduced in the 1940s, and they remained standard equipment throughout much of the rest of the 20th century. Today, halogen lamps are in use almost universally. First introduced in 1962, these brighter, longer-lasting headlights were available in the United States by the end of the 1970s. Halogen cartridges were first made available in the United States in the 1980s, and they are currently OEM equipment in most new cars.

Headlight Components

Traditionally, headlights all contained a few basic components, including a:

  • bulb
  • parabolic reflector
  • lens

The bulb is the source of the light, and it is typically either either incandescent or halogen, although a handful of other light sources are also in use. Some headlight bulbs contain two filaments (one for low beams and one for high beams), although others use only a single filament. In those cases, seperate low and high beam bulbs are used.

headlights components

The basic optical components of a parabolic headlight.

The parabolic reflector surrounds the light and focuses it toward the lens. When the light leaves the bulb, it is more or less omnidirectional. When it hits and bounced off the parabolic reflector, it is more or less aimed straight ahead. Then when it passes through the lens, it is refracted at a downward angle. That allows the light to illuminate the surface of the road without blinding oncoming drivers.

Modern headlights typically only include a bulb and a reflector. Rather than a simple parabolic reflector, these headlights use a multiple mirror reflector that directs the light at a downward angle without the need for a separate lens. Another modern innovation uses an elliptical reflector, a solenoid-operated shield to control the high and low beams, and a forward-mounted lens. These are known as projector, or polyellipsoidal, headlamps.

JD Laukkonen

JD Laukkonen turned wrenches in the north end of Seattle for a decade, so he's no stranger to the inner workings of modern automobiles. He has worked as a freelance writer since closing his shop in 2007, and he currently covers automotive technology for Lifewire.com.

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