10 Things You Need to Know About Headlights, Taillights, and More

Among the many things that buyers consider when selecting a new car, headlights have become increasingly important. That’s because there are more options in lighting than were ever available before, and more difference between the options.

The first headlights were used well over 100 years ago. They were simply candles or oil lamps in glass cases. They didn’t light up the road ahead of the car, but they allowed others to see where the car was. Electric headlights came along soon after, and that innovation allowed motorists to drive after dark. To help you understand headlights, taillights, and other lights on your vehicle, we’ve put together this short primer on the topic. Click through to become an expert.

In 1940, the 7-inch round sealed-beam headlight assembly became the standard for cars sold in America. Before that, a variety of plug-in light bulbs were used. The U.S. Department of Transportation mandated two of these headlights per car, with high and low beams in the same assembly.

Beginning in 1957, automakers could choose smaller 5.75-inch sealed beams with separate high/low and high beam units. That’s why many cars of the late ’50s suddenly got dual headlights on each side. In 1974, rectangular sealed beams were permitted, and that’s why cars of the ’70s got square headlight designs. But through the early 1980s, sealed beam lights were the only legal equipment. All things considered, sealed beams work pretty well. If you have an older car, you can find halogen sealed beam units, or upgrade to the later halogen lights.

Halogen headlights are brighter than the older sealed beam units, and they're easier to replace. The first halogen bulb, called the H1, was first invented in 1962, but these lights were not allowed as original equipment on American-market cars until 1983. Most cars made since 1983 have halogen lights, and more than 80 percent of vehicles on the road today feature halogen headlights.

The main thing to know about halogen lights is that there’s a replaceable light bulb that is placed inside a larger reflector or projector unit that focuses the light into a beam. Instead of disassembling the headlight to remove a sealed beam, a car owner can simply remove the bulb from the back of the assembly and replace it. One important tip: When replacing halogen headlights, handle them only by the metal ends. Don’t touch the glass, or the oils from your skin will shorten the life of the bulb.

Many vehicles made with halogen lights use clear plastic lenses to protect the reflector and the halogen bulbs inside. These plastic lenses tend to “fog up” over time, as UV light from the sun oxidizes the plastic and road grime puts tiny scratches in the surface. The lens becomes hazy and diffuses the light, making your headlights less effective.

When this happens, you can buy a new headlight lens, but that’s often too expensive to justify on an older vehicle. You can also purchase a headlight lens polishing kit, with some gentle abrasive polish. It doesn’t take long to polish the lenses and get back some clarity by removing the UV-damaged surface. Here’s a secret: You can also use ordinary toothpaste and a rag and it works nearly as well as the kit you get at the auto parts store. Just know that it’s a temporary fix. The lights will fog up again in a few months, so put this on your regular maintenance plan.

Starting in the 1990s, new high-intensity discharge (HID, or Xenon) headlights started to become available on premium brands. These lights are much brighter than anything that came before, but they’re also much more expensive and complicated.  

HID headlights make light by creating an arc between a pair of electrodes. If you think about an arc welder or that thing in Tony Stark’s chest in the Iron Man movies, that’s essentially what it is. HID lights are great for lighting up the road ahead of you with crisp, white light. However, if one of the units gets damaged in a collision or burns out, they are dramatically more expensive to replace than older units. 

The newest type of headlight commonly available on the market today is LED, or light-emitting diode. These lights have replaced HIDs on new cars because they’re just as bright and only a fraction of the price. LED lights use an array of tiny LEDs and then focus the beams forward. If you have the chance to buy a new vehicle with LED headlights, it’s a great investment. You can also get LED setups that plug into older HID or sealed-beam headlight assemblies.

One of the neat features of LED lights is that they can be made to change color. Most automakers don’t do this with stock equipment, but aftermarket kits can offer the ability to put a “halo” or “angel eyes” circle around your headlights and have the circle change color using a smartphone app. These are also known as “prism” lights. This may or may not be legal where you live, so check your local regulations.

Headlight tech is now moving faster than ever, and several automakers are developing new “Matrix” LED headlights that adapt themselves to oncoming traffic. Since the 1950s, cars have been able to use a light receptor to automatically dip their lights when other cars are approaching. But the matrix lights are able to redirect light to screen out oncoming cars, so the driver is not blinded by the LED headlights.

Audi’s Matrix lights use a digital micromirror device (DMD) that has up to 1 million micromirrors that can direct the LED light to the road or to an absorber, as needed. The system can use steering input data to direct light to the left or right during cornering, or even display patterns on the ground when the vehicle is stationary. 

Daytime running lights (DRLs) are simply less powerful lights that are on whenever a vehicle is running. The purpose of a DRL system is to make a vehicle more visible in daylight hours when the main headlights and taillights are not in operation.

DRLs have been available on U.S.-market vehicles since 1995. Some automakers such as GM have been putting them onto their vehicles since that time, while others have not included them or made them optional. As time has progressed, most new vehicles now include DRLs, and many offer LED DRLs. Note that many insurance companies offer discounts for vehicles equipped with DRLs.

Taillights, side and roof marker lights, brake lights, and turn signal lights have changed the least over time. For most of the last century, these were simply small incandescent light bulbs that are subject to burnout but are generally easy to replace. More recently, LED lights have become popular on all grades of vehicles.

One great upgrade to an older car is to replace the incandescent bulbs with LED bulbs. These fit right into the traditional sockets and give you bright LED turn signals, brake lights, or marker lights. Plus, the LED bulbs will last a lot longer than traditional bulbs. This is an affordable way to update the lighting on your classic car.

As the name implies, fog lights are low-mounted headlights that are designed to help illuminate the road in foggy conditions. Fog is a mist of water particles, and as most drivers have learned, those particles reflect bright headlight beams back at the driver. But fog generally floats a short distance above the ground, so a low-mounted beam projects further and does not reflect back.

Most states allow two forward-facing fog lights on a vehicle, with the rule that the fog lights operate only when the car’s low beams are active. If you switch on the brights, most factory-installed fog lights turn off. Check your state laws for direction if you’re installing aftermarket fog lights. 

Headlights and all other lights on your vehicle are one of the most critical safety systems you’ve got. It’s important to keep them working properly, especially on older vehicles where the lighting isn’t as effective to begin with.

Here’s an example of headlight safety. Most halogen reflector lights illuminate about 300 feet ahead of your vehicle. HID and LED headlights can light up about 400 to 450 feet, respectively. Depending on your vehicle’s brakes, however, it can take more than 500 feet to stop from 55 or 60 mph. That’s why it’s critical to keep your headlights in their best operating condition and not “overdrive your lights” at night.