How Headlights Are Tested and How Yours Can Be Improved

According to the Insurance Institute for Highway Safety (IIHS), about half of fatal roadway crashes happen in the dark, with about a quarter of those happening on unlit roads. This statistic makes it more important than ever to test and make sure that headlights work properly and provide the best visibility while driving at night. New IIHS testing has found many vehicles lacking when it comes to their headlights. Luckily, there are some steps you can take to improve the overall lighting that your car's headlights produce, making your vehicle safer to drive on the road.

How headlights are tested

In an effort to measure how far a vehicle's headlights reach in a variety of situations, the IIHS subjects vehicle headlights to five different approaches, including straight-aways, gradual left and right curves with an 800-foot radius, and sharp left and right curves with a 500-foot radius.

The measurements are taken on the right edge of the roadway during each vehicle approach, as well as on the left edge of the lane of travel when testing light reach on curves. For straightaway testing, an additional measurement is taken on the left edge of a two-lane road. The purpose of these measurements is to gauge the illumination level on both sides of a straightaway.

The glare from a vehicle's headlights is also measured. This is particularly important as the glare from oncoming vehicles must fall below a certain level. For the most part, there is a steep drop off in light emanating from the left side of most vehicles.

In order to determine visibility levels, measurements are taken 10 inches from the ground. For glare, measurements are taken three feet seven inches from the pavement.

How IIHS headlight safety ratings are given

The engineers at the IIHS compare the measurements they gain from testing against a hypothetical ideal headlight system. Using a demerit system, the IIHS applies the visibility and glare measurements to come up with a rating. To receive no demerits, a vehicle must not exceed the glare threshold on any of its approaches and must illuminate the roadway ahead by at least five lux over a given distance. In this testing, the low beams are weighted more heavily due to the likelihood of their use over high beams.

Headlight ratings. The IIHS headlight system uses Good, Acceptable, Marginal, and Poor ratings.

  • To gain a Good rating, a vehicle must not get more than 10 demerits.
  • For an Acceptable rating, the threshold lies between 11 and 20 demerits.
  • For a Marginal rating between 21 and 30 demerits.
  • A vehicle that gets more than 30 demerits only qualifies for a Poor rating.

Top-performing cars when it comes to headlights

Out of 82 midsize cars only one, the Toyota Prius V, earned a Good rating. The Prius uses LED lights and has high-beam assist. When only equipped with halogen lights and without high-beam assist, the Prius only got a Poor rating. In essence, it would seem the headlight technology a vehicle uses plays a part in the rating given. On the other hand, this is at odds with the 2016 Honda Accord, with Accords outfitted with basic halogen bulbs receiving an Acceptable rating, while Accords with LED bulbs and using high-beam assist only rated as Marginal.

Some other 2016 midsize cars that received an Acceptable headlight rating from the IIHS include the Audi A3, Infiniti Q50, Lexus ES, Lexus IS, Mazda 6, Nissan Maxima, Subaru Outback, Volkswagen CC, Volkswagen Jetta, and the Volvo S60. Most vehicles that received an Acceptable or better rating from the IIHS for their headlights require car owners to purchase a certain trim level or various options.

How to improve your headlights

While you might think you are stuck with whatever headlights your vehicle manufacturer put on your car, you can actually upgrade them. A few options exist that can improve the light output of your vehicle's headlights, including adding additional light sources to your vehicle or changing the brightness of the headlights themselves by replacing the headlight enclosure to a more reflective one.

Purchase external driving lights. Adding additional light fixtures to the body of your vehicle is one option when trying to improve your vehicle's headlights.

This is a great option if you want to add fog lights or lighting for when you go off-roading.

This often requires you to drill into the body of your vehicle, which could lead to rust formation in wet environments.

Another consideration when adding lights to your vehicle is the extra load it could place on your battery. At the very least, you may have to install another relay.

Replace your headlights with brighter bulbs. You can change out your standard halogen headlight bulbs for xenon high-intensity discharge (HID) bulbs or LED bulbs.

  • Xenon HID and LED bulbs produce a brighter light than regular halogen bulbs while producing far less heat.

  • HID and LED headlights also produce a larger pattern when compared to halogen.

  • HID bulbs tend to produce more glare, making them harder on other drivers.

  • LED bulbs offer great lighting but are cost prohibitive when compared to other bulb types.

Replace the headlight enclosure. Another option is to change out the headlight enclosures in your vehicle with ones that are more reflective, thus magnifying the light produced.

Reflector enclosures use regular halogen or xenon bulbs to produce more light.

  • Warning: Keep in mind that if you modify your existing headlights, you need to make sure they are aimed correctly. Incorrectly aimed headlights can actually reduce visibility and blind other drivers on the road.

You are not stuck with whatever headlight system your vehicle manufacturer installs in your car. You do have options to improve your lighting situation while driving. The IIHS tests and rates vehicle headlights to try and improve vehicle safety and can give you a better understanding of this emerging area of vehicle safety. If you need help replacing your headlights, contact one of our expert mechanics.


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