Federal rule limiting headlight brightness may not effectively address LED technology.
Anyone who has recently driven at night can attest to experiencing an overwhelming light burst from an oncoming vehicle’s headlights. This glare phenomenon is more than a nuisance—it impairs a driver’s vision temporarily. The federal agency tasked with preventing car accidents, the National Highway Traffic Safety Administration (NHTSA), reportedly receives more complaints from consumers about headlights than any other topic.
Drivers are not imagining things. Most new headlights now use light-emitting diode (LED) technology that shines at least four times more brightly than traditional halogen bulbs. They also produce more blue wavelength light than halogens. People who view bluish LED light report increased visual discomfort.
Charged by law with issuing automobile issues motor vehicle safety standards, NHTSA quantifies headlight brightness in candelas, which measure the intensity of light emitted in a particular direction. Brightness limits vary depending on whether the beam is high or low, the vehicle type, and specified points at which the headlight is angled. Testing for headlight compliance with NHTSA standards occurs in a controlled laboratory setting.
Newer headlights may meet the standards in a laboratory but still feel too bright because LEDs work differently than older halogen lights. LED headlights function more like a computer screen, with individually illuminated pixels than like a traditional light bulb with a general glow. This feature provides more concentrated brightness and sharper edges of light—think of the crisper shadows that LED streetlights cast compared to the softer shadows of incandescent streetlights. At night, these sharp edges from LED headlights pierce vision more intensely than halogens, particularly when combined with the bluish tone of LEDs.
NHITSA only recently issued an amendment to its vehicle lighting rule to allow for a new form of headlights called adaptive driving beams. These automatically dim the high beam part of headlights when vehicles approach. In the amendment, NHTSA set glare limits for adaptive driving beams that would address the blinding effects of headlights on oncoming drivers in a dynamic driving environment.
NHTSA measured these glare limits in lux, which quantify overall illumination of a surface, and not candelas, which are used to measure beam strength in a particular direction. The Insurance Institute for Highway Safety uses lux to evaluate headlight glare for its consumer safety ratings because it believes the unit better captures how light is experienced in real-world driving conditions. NHTSA amended its vehicle lighting rule to include glare limits, set in lux, for adaptive driving beams. The rule defines no glare limits for standard headlight types, however. Because adaptive driving beams are mostly limited to luxury car brands such as Audi and Mercedes, glare limits do not apply to many cars on the road currently.
Adaptive driving beams may not eliminate the bright headlight problem. The Soft Lights Foundation, a consumer safety organization focused on the harms of LEDs, claims that adaptive driving beams do not address the excessive brightness of low beams in standard headlights. The “adaptive” element only dims the high beam and does not modify low beams. One reporter suggested that the updated NHTSA headlight rule still fails to restrict the different, harsher way LEDs transmit light in contrast with older halogen lights.
This issue has garnered some congressional attention—in July 2025, U.S. Representative Marie Gluesenkamp Perez (D-Wash.) proposed legislation that would fund a study on the impact of headlight brightness. She previously urged the U.S. House Committee on Transportation and Infrastructure to change the maximum brightness standard to better reduce glare on the road.
Several other factors contribute to glaring headlights on the road. One factor that NHTSA has raised relates to LED headlights which are separately purchased and installed by consumers. NHTSA noted that, although these lights may exceed permissible brightness limitsthe agency typically “does not regulate the modifications individuals make to their own vehicles,” leaving the matter to be addressed by state law.
Headlight misalignment and height also play a role. A slight change in the angle of a headlight causes a large difference in the field it illuminates. Upward mis-aim of one degree can increase glare intensity to oncoming drivers by a factor of eight. This misalignment occurs as part of normal wear and tear on a vehicle but only ten states require headlight alignment checks during vehicle inspections. In addition, the headlights on SUVs and other tall vehicles sit higher, so their beams shine directly in the sight line of drivers in shorter cars. In its final rule concerning adaptive driving beams, NHTSA acknowledged the “unique” compliance challenges associated with high-mounted headlights and suggested that manufacturers aim headlights lower or alter the arrangement of lights to avoid glare.
Regulators will have to reckon with the harsh nature of LED light, aftermarket bulbs, and misaligned headlights if they are to address the blinding brightness plaguing many U.S. drivers each night.
