The Reason Old Cars All Had The Same Headlights

Over the next few decades, America changed. The automobile became more commonplace, cities grew, and the “suburbs” became a thing. People went from driving in the city, to driving on rural roads at night where street lighting wasn’t available. Thus, headlights became far more critical. During that time, all manner of headlight innovations sprung up, without standardization. Finding a replacement lamp during this era was impossible, until a paradigm shift occurred.

In 1939, the sealed beam headlight was created. It consisted of a tungsten filament bulb soldered into the middle of a metal reflector, with a glass lens fastened to the front. It was basically an “evacuated glass envelope” that could better narrow the light into a focused beam. It quickly became the de facto headlight design, because the following year, the federal government mandated that all new vehicles sold in the United States needed to have two 7-inch, sealed beam headlights. For the next 17 years, every car, bus, and truck made used the same round 7-inch headlights, which (accidentally) stagnated car designs for almost two decades (via 1000Bulbs).

The law wasn’t changed until 1957, and only then did the government allow the use of four round, sealed beam headlights instead of just two — with each of those having a smaller 5 3/4-inch diameter. One acted as a dual filament lamp like the original, while the second came with a single high-intensity filament for high-beam use.

Rectangle headlights weren’t introduced until the 1970s. However, they were still the same sealed beam headlights (via Technology Connections), which remained the status quo until 1984 when the Ford Lincoln Mark VII became the first car to use the new and differently shaped aero lights.