The real reason behind blinding headlights

Complaints keep circulating about the lights coming on at night. No, it isn’t about just any lights; it’s about headlights. It seems that vehicle headlights, year after year, get brighter and brighter. And many people are asking what can be done to dim these lights.

There are three types of headlights: standard halogen (which are most common), high-intensity discharge or HID (which came in around the 90s) and LED (light emitting diode) highlights (which are found in a lot of newer vehicles). Each lighting type is measured by candlepower and lumens. They each measure different light qualities, and one candlepower equals 12.57 lumens. When measuring lumens, it refers to the light illuminated in a one-square-foot area one foot away from a single candle.

Utah Code states, “A lighted lamp or illuminating device on a vehicle, which projects a beam of light of an intensity greater than 300 candlepower, shall be directed so that no part of the high intensity portion of the beam will strike the level of the roadway on which the vehicle stands at a distance of more than 75 feet from the vehicle.”

A technical report from 2004 titled “Drivers’ Perceptions of Headlight Glare from Oncoming and Following Vehicles” gives some perspective. The report reads as follows:

“Recently, U.S. drivers have been expressing concern over the discomfort and reduced visibility that they experience from headlight glare from other vehicles. Drivers have focused their concern on the relatively new high intensity discharge lights, high mounted lights and various auxiliary lights. In order to better understand this glare problem, the National Highway Traffic Safety Administration collected data on drivers’ perception of glare from a representative sample of U.S. drivers. The survey was conducted through Omnibus Survey of the Bureau of Transportation Statistics. The present study is based on the information (data) collected on two types of glare: glare from oncoming and following vehicles. 

“The survey data were analyzed to find out how U.S. drivers perceive the two types of glare and if glare perception is associated with respondents’ age and gender. Contingency analysis was conducted to establish these associations. The statistics showed that a sizable number of respondents feel that glare was ‘disturbing.’ It was found that the age group 35 to 44 had the highest percentage of night drivers as well as among those who felt glare ‘disturbing.’”

Basically, the survey found that 88% of drivers noticed headlight glare, with 31% saying the glare is “disturbing.” While headlight intensity may extend the visibility of objects ahead of drivers, the glare also seems to increase the discomfort of other drivers and pedestrians. This glare can also reduce visibility by reducing contrast or causing drivers to turn away from the roadway to avoid any eye discomfort.

Science explains why LED lights seem so much brighter than halogen. This phenomenon is called color temperature. While many may think lights are clear, each light has a spectrum ranging from orange-yellow to blue-white. The brighter the light, the bluer the light. LEDs and HIDs hit on the blue-white spectrum where the halogen is closer to the orange-yellow.

Studies have found that these blue-white lights tend to hit people’s eyes harder, especially in the dark. Those cooler color temperatures can be blinding but are also helpful when behind the wheel as they illuminate farther distances. And, when it comes right down to the science, these bluer lights are not actually brighter than the yellow spectrum.

Some auto repair shops say factory lights are typically brighter than after-market. These after-market lights have simply been changed from the original factory model. The most common cause of visually brighter lights is that they have not been appropriately adjusted for that vehicle. They are also difficult to calibrate due to not having an environment in which to adjust (not dark enough or long enough spaces to test them). The worst part? Enforcement is difficult as there are no reliable ways to measure these lumens.