Curious Iowa: Why are some vehicle headlights so much brighter than others?

It’s easy to spot the difference at night. Some headlights are brighter than others. And for some drivers, those brighter headlights may seem more blinding.

Alan Makabi, digital marketing manager at Cedar Rapids Toyota, said the difference is the type of headlight. LED headlights, which usually are the brighter lights, are found on higher-end, more expensive vehicles. And those headlights’ popularity is growing.

“You're going to see more and more vehicles going to the LED brighter light. When you're heading down the road, and you see opposing traffic coming, and you see that kind of bluish look, that's the lights you're seeing,” Makabi said. “Mostly, it's from a visibility standpoint that the LEDs are becoming more and more common here lately, and also the longevity factor of an LED light.”

The difference in headlight brightness caught the eyes of two local residents. They sent their question to Curious Iowa — a series from The Gazette that answers readers’ questions about the state and how it works.

“Why are headlights on cars and trucks different colors and brightness?” the readers wondered. “Who determines the brightness of the lights?”

The Gazette spoke local experts and did some research to find the answers.

What are the different kinds of headlights seen on vehicles?

There are three main types of headlights, Makabi said. The most common are halogen bulbs, which appear as yellow-white headlights.

The brighter blue-white lights that have become more common are either LED — or, light-emitting diode — bulbs, or HID bulbs, which are high-intensity discharge. LEDs and HIDs are similar in color and brightness, but LEDs tend to last longer and cost more.

“Most of the cars, regular cars, are coming with halogen, but in the upper end models, they'll come with these LED, HID lights,” Makabi said.

According to AAA, which has researched LED headlights and their effect on driver safety, the lights are not necessarily brighter, but the light emitted by the bulbs can be more irritating to the human eye.

The association for years has advocated for the use of adaptive driving beam headlights. The technology, which has been used in Europe and Canada for years, automatically adjusting the brightness of headlights when oncoming cars, pedestrians or other figures are detected. The technology was approved by U.S. regulators in 2022, but so far it’s only available in luxury vehicles.

Is headlight brightness regulated in Iowa?

While there are federal laws that specify the maximum and minimum luminosity allowable for headlights produced by vehicle manufacturers — meaning that any headlights that come with a vehicle sold at a dealership will already have been tested and approved to meet the requirements — Iowa’s code is a bit less specific, simply stating that headlights should be “directed high enough and of sufficient intensity to reveal people and vehicles at a safe distance in advance of the vehicle.”

The code also specifies the required number of lights required: two on the front and two on the back for cars, and one or two on the front and back, for motorcycles. Code also set allowed colors — yellow, white, or amber on the front, and red on the back.

Iowa law also requires that the lights not be directed so high as to be projected into the eyes of an oncoming driver, something Alex Dinkla, public information officer for the Iowa State Patrol, said is regularly enforced through traffic stops.

“You can definitely tell when headlamps are out of adjustment, whether they’re pointing right into you, or oftentimes you can actually see the way the beam is facing on the road, or into the ditch, if they’re improperly adjusted,” Dinkla said.

Other headlight problems Dinkla said may result in a traffic stop include a headlight or taillight not working, or if there are extra lights on a vehicle.

“Some folks like to drive with those auxiliary lights, like a light bar, either on their grill or on top of their car. That is something that you cannot do,” Dinkla said. “Those are meant for off road use, not on road use.”

Newer vehicles also sometimes have headlight features that cause problems if drivers aren’t aware of them, like daytime running lights or a feature that automatically turns on front headlights, but leaves taillights off. Dinkla said he often stops drivers who have their car’s headlights on but the taillights are off, so it’s difficult to see their car from behind at night.

Dinkla said he also often reminds drivers to turn their lights on when there are adverse weather conditions, like fog, rain or snow.

“It may not always be something that is beneficial for you, for visibility, for you to see, but it’s going to make your vehicle able to be seen by other vehicles,” Dinkla said. “So, it does lead to a good safety reminder that turning those headlights on in low light or weather conditions can add to your safety.”

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Comments: (319) 398-8328; emily.andersen@thegazette.com