Lighting Do New Vehicle Headlights Cause More Glare?

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More and more people feel dazzled by vehicle headlights. Is this just an illusion, or is new technology contributing to it?

More and more people increasingly feel dazzled by the headlights of oncoming vehicles in the dark. So many and so often, in fact, that Europe's largest automobile club felt compelled to dedicate an entire international symposium to the topic of glare.

The background for this was a prior Europe-wide survey among drivers and road users. According to the survey, over 70 percent of German drivers sometimes or regularly feel dazzled. Interestingly, 32 percent of respondents under the age of 35 feel almost always or regularly dazzled, whereas this figure drops to just under 23 percent for those over 50. The survey thus debunks the notion that glare is primarily a problem for older drivers—the opposite is true.

"Bright As Daylight"

The culprit is quickly identified: for years, the number of vehicles using LED technology to produce their headlights instead of traditional halogen or now outdated xenon technology has been rising. As Osram advertisers once phrased it, they are "bright as daylight." While this is delightful for those behind the wheel, it is equally annoying for those facing such an "LED dazzler" coming from the opposite direction.

Many now demonize the technology of light-emitting diodes, just as gas discharge lamps were about three decades ago. Is this comparison valid—and especially the conclusion that the then-new technology objectively did not cause any more glare? In other words: Are the alleged causes of glare the same, or are there different ones?

Glare Has Many Causes

These and many other questions were answered by numerous experts during the 1st ADAC Glare Symposium: ranging from the function of the human eye, the role of glare as a cause of traffic accidents, and methods for measuring glare, to the dependencies on the size and luminance of an LED light source and the influence of road surfaces and the level of dirt on headlight covers.

The fact that a large organization like ADAC, together with automobile clubs from other countries, felt compelled to hold such a symposium demonstrates the extent of the problem by now. "The number of complaints about 'light cannons' and doubts about the legality of these 'intolerable, novel light sources' has increased massively in recent years," stated Burkard Boettcher, technical advisor for vehicle technology at the ADAC Technology Center in Landsberg, Germany.

A Gap in the Law Promotes Glare

To examine the objective validity of these subjective impressions, it is necessary to "shed light" on the changes in lighting technology, especially in comparison to xenon technology. For instance, the light temperature of LED lights has changed. While it is a warm 2,700 Kelvin with halogen lights, it is already a cooler 4,000 Kelvin with xenon and 6,000 Kelvin with LED. Similarly, the light color spectrum has changed—it has become even bluer.

Additionally, automated lighting functions such as low beam or high beam strain the eyes of oncoming drivers; for instance, adaptive high-beam systems that switch in nanoseconds—but often only after seconds, or not at all.

Higher Luminance Can Promote Glare

One of the main reasons for glare from LED headlights, alongside light intensity, is the luminance. It is often significantly higher than that of xenon lights and continues to rise. This is because the headlights or light-emitting surfaces of modern vehicles are becoming increasingly smaller. The culprit is essentially a regulatory gap, as the UNECE regulations responsible for the approval of vehicle lights simply do not define or regulate luminance.

They only do so in terms of luminous intensity, meaning the absolute amount of light without reference to the size of the light source. However, the human eye perceives using luminance, which is why the size of the light source affects its impact on the retina.

Smaller Areas With More Direct Light

Another significant difference: With xenon headlights, the oncoming eye never looks directly into the source, as the light produced by the burner is distributed by a reflector and then passes through a lens system—similarly with later halogen systems. In contrast, with LED lens systems, people often look directly into tiny fields of extremely bright LED chips.

What further strains the human eye: It often has to register multiple different light fields, as LED headlights are often composed of several such fields.

Light Distribution of Sedans And SUVs

But there is another factor contributing to increased glare—particularly with regard to "dazzling" LED lights: the vehicle type. This means that while the distance from the center of the headlights to the road, as determined by TU Darmstadt (Germany), averages just under 27 inches for sedans and up to the lower edge of the windshield around 33 inches, the former is significantly above 35 inches for SUVs.

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In other words: An SUV headlight shines directly onto the upper body/head of an oncoming sedan driver. Thus, this vehicle category not only negatively impacts the accident safety of other road users but also increases glare.

Glare Source: Dirt on Headlights

What drivers of all vehicles can directly influence, however, is an entirely different source of glare: the one caused by dirt on the headlights. How strongly this causes or promotes dangerous light scattering was demonstrated in experiments by Tran Quoc Khanh, also from TU Darmstadt (Germany), back in 2017.

Thus, dirty headlight covers of an oncoming vehicle at a distance of five meters increase the light intensity by a factor of six to seven.

This is What Experts Demand for Vehicle Lighting

And so, the various wishes and demands raised by the speakers at the Glare Symposium towards legislation come as no surprise. One measure is as understandable as it is simple to implement: narrowing the permissible tolerance range for headlight adjustment. Henrik Liers from the Traffic Accident Research at TU Dresden (Germany) called for a tightening from ±0.5 percent to ±0.25 percent. "This would reduce the number of vehicles with headlights set too high from 25 percent to 8.9 percent," explains Liers.

Tomasz Targosinski from the Motor Transport Institute in Warsaw, Poland, outlined several understandable demands to the UNECE with regard to vehicle manufacturers. Among others:

• The separation of "real" and "decorative" lamp elements, for which different requirements should apply.
• Lighting regulations should include detailed requirements that can be checked during the main inspection.
• Limit values for measurements should be clearly defined and enable an objective assessment of all light control functions, including the actual alignment and leveling.
• Glare should be verifiable during traffic controls.

Workshops And Headlight Adjustment

The topic of "correct headlight adjustment" is correspondingly more important today than ever before. That is why Michael Hamm from TU Darmstadt rightly referred to his institute's 2016 study. It found that only one-tenth of all headlights were correctly adjusted according to UNECE standards straight from the factory.

Additionally: When headlights are later inspected and adjusted in practice, for example during service or the main inspection, many responsible parties fail to properly condition the vehicle, says Hamm.

A load of 880 pounds in vehicles without or with defective automatic leveling completely reverses the dip of the low beam: from -1 percent to +1 percent, resulting in full glare. The same applies to the fuel tank. A correctly adjusted low beam with an empty tank deteriorates by an average of up to 1.75 percent when the tank is full—unless it is automatically or manually corrected by the driver. And this brings us to the human error factor—even outside the vehicle.

A test conducted by TU Darmstadt involving eleven workshops assigned the task "check and, if necessary, adjust headlight alignment" revealed some concerning findings: Only three workshops were able to correctly adjust two misaligned headlights, six failed, and two did not even touch the headlights.

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