How Headlights Work?

By lisa | 10 June 2020 | 0 Comments

How Headlights Work?

How Headlights Work

All headlights illuminate the road ahead in one of two ways, Stockburger says. The first, traditional way is to use a reflector to bounce the light from the bulb forward. The other way is to use what is known as a projector, where the headlights use a lens that focuses and directs the light outward.

Halogen headlights
There are several ways for headlights to create illumination. Halogen bulbs heat a filament to the point where it emits light. They’re the most common on U.S. roads, and they typically give off a yellowish tint.
HID headlights are less common, and they work by igniting a gas—most often Xenon—with electricity inside a bulb. They emit a white or bluish-white hue.

High-intensity discharge (HID) headlights
LEDs are a far more advanced technology. There are two semiconductors (on a small chip) with either a surplus or a small number of electrons. When the two semiconductors have an electrical charge applied to them, atoms move toward each other and combine, and the resulting energy that's created is released as light.
Light emitting diode (LED) headlights
The Move to LEDs
LED headlights first appeared in the U.S. on the Lexus LS 600h sedan back in 2007, and they were originally found only on high-end cars. But LEDs began appearing in more mainstream models about eight years ago, and some of them impressed us in our testing.
Why the swing? There are several factors at work.
Headlight styling helps win over consumers, says Steffen Pietzonka, head of marketing at Hella, a headlight manufacturer. “The different looking headlights and design are attractive to the buyer because the headlights are the eyes of the car,” he told LITU LIGHT.
In addition, LEDs are supposed to last far longer than the other two types of lights, which is a convenience and potential money saver for owners who plan to hold onto their car for the long haul. Last, LED bulbs use less energy than both halogen and HID lights, they run cooler, and they’re less of a drain on the vehicle's electrical system. Ron Kiino, communications manager at Subaru, says that means there’s the potential to save money on gas as well.
According to Pietzonka, “HIDs may be out of the market quite soon, because there are lower-cost options.” He adds that “in Europe, every new [car] development project in the industry has no HID/Xenon systems in the pipeline. In the U.S. it will be similar, with HIDs out in the midterm.”

What LITU LIGHT Has Seen in Testing

Both LED and HID headlights can produce a brighter, whiter light than halogens, and they illuminate the sides of the road well. But how far a headlight illuminates straight ahead, in the direction a car is traveling, is what’s most important, Stockburger says. In that respect neither HIDs nor LEDs have proved to be superior over halogens in LITU LIGHT’s testing.
“Even with the new technology, low-beam headlights don't always provide enough forward seeing distance for the driver to react to an object in the road and stop in time,” Stockburger says.
For example, LITU LIGHT’s brake testing shows that, on average, a vehicle traveling at 60 mph (or 88 feet per second) on dry asphalt in ideal conditions needs about 130 feet to come to a complete stop. Estimates for a driver’s reaction time between seeing something ahead in the road and hitting the brake pedal is 2.0 seconds—at roughly 88 feet per second, the vehicle has traveled 176 feet before the driver has hit the brakes. That means the total distance needed from recognizing an object to coming to a full stop is about 300 feet.
But in our headlight tests, we’ve seen that neither LED nor HID low-beam headlights consistently illuminate more of the road ahead than halogens do. The poorer performers among all headlight types don’t reach the 300-foot mark. The result is that drivers traveling at 60 mph or faster will “overdrive” their headlights, meaning they're going faster than the lights can illuminate the road ahead, giving the driver little time to stop. The Escalade we tested in 2015 was able to illuminate signs on our headlight test course as far as 400 feet ahead.

Learn how LITU LIGHT tests headlights.

“We’ve found that with LEDs and HIDs, manufacturers are having a hard time balancing casting enough light down the road without causing glare to oncoming drivers because of their intensity,” says Stockburger. “Many oncoming drivers mistakenly think an oncoming vehicle has its high beams on, when in reality the car just has LEDs or HIDs.” This is particularly a problem with oncoming SUVs, because their headlights are positioned higher up on the body than on a car.
You don't automatically get a better system when you use LEDs, Hella’s Pietzonka says. "If you have a bad optical system or a bad reflector, then the LEDs can’t produce better light,” he says.
Cost is also a factor. The automaker decides how many lumens (a measurement of brightness) it wants out of its lights. For example, a headlight assembly with two LEDs may perform worse than a halogen light, one that has three LEDs may equal the performance of a halogen light, and a unit with five LEDs can exceed the performance of a halogen light, but ultimately it's a matter of how much money a manufacturer wants to spend, Pietzonka says.

What Consumers Should Do

It’s important to “try before you buy,” and that includes a car’s headlights, Stockburger says. Shoppers should test drive the vehicle they’re interested in at night. Make sure the test car is equipped with the type of headlights that will be on the car they’re considering. For example, it isn’t helpful to test drive a car with halogen headlights if the desired version only has LEDs.
Buyers shouldn’t be swayed by the style of the lights or the idea of getting some cool new tech.
And owners should always be aware that headlight alignment is important regardless of the underlying technology. Headlights should be aligned vertically so that the road ahead is properly lighted, but also so that glare to oncoming drivers is limited. They should be aligned by a mechanic whenever the light assembly has been removed and reinstalled, such as after a repair.
In addition, owners of a brand-new car should bring the car back to the dealership for a headlight alignment if they feel that their headlights aren’t properly illuminating the road ahead. We buy every vehicle we test from dealers for evaluation at our Auto Test Center and often have to adjust the headlight alignment on test cars before evaluating them, Stockburger says.
It’s particularly important for used-car buyers to make sure the headlights are aligned. If there is any doubt, have the dealership do it, or insist that the sale price be lowered to cover the cost of a headlight alignment.
Jill Trotta, a vice president at RepairPal, a website that estimates auto repair costs, says that on many models “the headlamps usually only need adjustment when there is an accident or something that might cause the actual assembly to move.” She says that it shouldn’t take more than an hour to get them realigned and will cost roughly $115 to do.
Some of this maintenance may be unnecessary in the future. “We’re trying to introduce systems, sometime in the future, where the end consumer doesn’t have to worry about the alignment of the headlights,” Pietzonka says. That includes creating systems that will automatically adjust themselves based on factors such as how the car sits when it’s loaded with people and cargo.

Advances Are Coming

Automakers have introduced some new features that make better use of headlights, and more are on their way.
At LITU LIGHT, we’re particularly fond of cars that have automatic high beams. This technology can automatically shift between low and high beams when appropriate. Research from the Insurance Institute for Highway Safety has shown that drivers opt for high beams less than half of their time spent driving, Stockburger says. This feature keeps the high beams on as much as possible, which gives drivers better visibility farther down the road in the dark without blinding oncoming motorists.
Another new technology, adaptive driving beams, is already used in Europe. The high beam headlights are constantly illuminated, but the system shuts off select LEDs to reduce glare and shield the eyes of other drivers when it detects oncoming headlights or if the car is approaching a vehicle ahead of it. GM’s Leinert told us that these lights “could improve visibility, as the higher output of LEDs puts more light on the road with more precise performance.”
This technology is not yet available in the U.S. because it doesn’t comply with current Federal Motor Vehicle Safety Standard 108, which governs headlight performance. Changes to those rules were proposed in 2018.
It’s high time we use them here, says Hella’s Pietzonka. “Regulations are not allowing the implementation of these new technologies, which have been on the road in Europe since 2010, almost 10 years.”

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