Have you ever driven down a roadway at night and looked into your rear-view mirror, only to be blasted by the super bright headlights of the vehicle behind you? If you have, you already know first-hand of one of the downsides of advanced headlight technology: having what feels like some of the power of the sun directed right at your eyes. Conversely, if you’ve driven a vehicle with newer headlight technology, you’ve probably really appreciated that the headlights are brighter, farther reaching, and able to provide a greater consistency or spread of light.
The Evolution of Headlight Systems
Advancements in headlight technologies have been driven by the desire to increase visibility while also reducing energy usage, so headlights have come a long way from the late 1800s, when the first electric headlamp was introduced. Halogen headlights were brought in the year 1962, and then HID (high intensity discharge, also called xenon or bi-xenon) headlights first appeared in 1991. LED (light emitting diode) headlights came out in 2004, followed by the most recent innovation – laser headlights, in 2014. Compared to LED headlights, laser headlights are smaller, can illuminate twice as far (up to 600 m using high beams), and are 30% more energy efficient. Night vision technologies that use infrared cameras and motion sensors to detect pedestrians and animals have also been recently introduced. Adaptive headlights are yet another new thing – they are able to adjust the headlight beams to “turn” along with the vehicle through a curve, and they also adjust the headlight position when the vehicle is braking or accelerating. These technological advancements are not without their hefty pricetags; HID headlights are more complex than halogen headlights, and hence, more expensive. LED headlights generate heat and need their very own cooling systems – making LED headlights even more expensive than HID headlights. Laser headlights are even more complex and hence the most expensive.
Headlights & Pedestrian Visibility
Considering that more than half of all traffic deaths occur at night, these newer headlights are one step in the right direction. As reconstruction experts, we are often called upon to reconstruct night-time collisions, including incidents that involve collisions with pedestrians. Commonly, we are also asked to determine whether or not the driver could have avoided the collision. As part of our analysis, we attend the collision scene during similar night-time conditions, and take illuminance and luminance measurements, using an exemplar vehicle and a pedestrian test subject (wearing similar clothing as the involved pedestrian). Illuminance is a measure of the amount of light falling on a surface, and indicates how well an area is lit. Luminance is a measure of the amount of light reflected or emitted from a surface, and indicates how bright a surface will appear. From the luminance measurements, we can determine the contrast, which is the difference in brightness between the target and the background. Contrast is important because our eyes rely on it to help us identify objects. Based on these measurements and observations gathered during our night-time scene examination, we determine when the pedestrian could have likely become visible to a driver; this directly affects the results of our avoidance analysis (where we assess if a typical driver could have been able to avoid the collision).
Implications for Collision Avoidability
For collisions that occur in suburban, rural areas or otherwise unlit areas, the vehicle’s headlights are one variable that can considerably affect pedestrian visibility. A vehicle equipped with older halogen headlights can illuminate a distance of up to about 65 meters (low beam setting), whereas a vehicle equipped with HID headlights can illuminate a distance of up to about 95 meters (low beam setting). To use an example, consider a vehicle travelling down a roadway at 50 km/h. If a pedestrian is walking in the same direction within the roadway about 100 m directly ahead of the vehicle, that pedestrian would become visible to the driver of the vehicle with HID headlights about 2 seconds sooner than they would have if that vehicle was equipped with halogen headlights. In other words, by driving a vehicle equipped with HID headlights in this scenario, a driver could have had about 2 seconds more of available time to perceive and respond to the pedestrian, making a collision less likely, or less severe. So, headlights that are brighter, farther reaching, and able to provide a greater spread of light may be effective in reducing pedestrian nighttime collisions.
It is worth noting that although a vehicle equipped with advanced headlights could allow a driver to potentially see a pedestrian earlier, research shows that pedestrians still seem to over-estimate drivers’ visibility of them. With all other variables being equal, a pedestrian wearing bright or white clothing is likely to be detected a distance of about 50% longer in comparison with dark clothing. Pedestrians can help increase their safety by wearing bright (and if possible, reflective) clothing when walking at night.
Forensically Determining Headlight Usage
Headlights only help increase a driver’s visibility at night if they are turned on. In claims where headlight usage is in question, there are several ways of forensically determining the truth. Although halogen headlights do not illuminate a distance as far as HID headlights, they have some forensic benefits: their filaments could be forensically examined for “hot shock” to identify whether or not they were on during a crash. Given that HID headlights are much more complicated in their design, including the use of specialized materials, identification of their use cannot be determined by examining their filaments, however, information on their usage may be retrieved from the vehicle’s EDR (Electronic Data Recorder) data, if preserved after a crash.
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