It wouldn’t surprise anyone that about half of deadly automobile accidents occur during nighttime hours. What is not common knowledge is that driving at night only accounts for 25 percent of overall traffic in the U.S. It’s intuitive that when driving in the dark, if one can’t see another vehicle, animal, pedestrian or curve in the road, bad things can happen. Seeing the road ahead at night has been a challenge since the advent of the automobile. Just as the automobile has evolved, so too, have the lighting systems that provide the means to see danger, while navigating highways in the dark.
History
Headlight technology has followed the same path as the development of the automobile. When cars were first introduced there was no precedent as to how they were designed, built, and what technology could be used to solve engineering challenges. Consider the early systems used to deliver fuel to internal combustion engines. One of the first (in the year 1875) was the rotary-brush “Atomizer,” where a pully-driven, rotating brush swept gasoline from a reservoir throwing it into a pipe and, suction from the engine’s pistons drew fuel/air into the combustion chamber. This idea and others gave birth to the carburetor that in some form, was in use from 1882 to the mid-1980s. Then, electronic fuel injection was widely introduced, eventually replacing the carburetor.
As you will see, automotive headlight technology has followed a similar trajectory: lots of “weird” ideas were tried in the beginning and, distilled down to the most practical solution, remaining the same for more than 50 years. Then, with advances in electronics, the technology undergoes radical changes. We'll take a look back at the early headlight, or headlamp technology; the current systems in use today, and cutting-edge headlights of the near future.
Used on carriages drawn by horses and early automobiles, oil, kerosene, and acetylene types of lamps provided lighting. Acetylene was the superior light source but using it was not exactly convenient. To turn on the lamp one had to open a supply valve, open the cover of the lamp and light a match to ignite the acetylene. Acetylene gas was produced in a tank (not part of the lamp) divided into two sections that had to be filled with calcium carbide and water, before using the vehicle. During winter months, alcohol had to be added to the water to keep it from freezing.
In 1912, Cadillac used one of the first electric headlamps for autos. An electric light bulb was used in place of an open flame and located between a polished reflector and glass lens. This design was flawed as, the reflector quickly rusted (since the lamp was not sealed) causing the light to become dimmer and forming a halo-effect around the light which blinded oncoming cars.
For electric automotive lighting to operate, a DC generator (dynamo) was required. The Cadillac Model 30 and Rolls-Royce Silver Ghost (premium cars) were some of the first automobiles that could produce the electricity needed, to support electric headlights. It wasn’t until the introduction of the electric starter (on the Model T) where a battery charged by a dynamo was widely used to power automotive lighting. By the 1920s, batteries were in use in a majority of cars providing power for electric headlamps.
With more cars on the road, driving at night became problematic because the headlights from oncoming cars would blind their drivers. The “dipped-beam” aka, passing, low or meeting beam provided drivers a way to direct headlight illumination away from oncoming traffic. In 1919 “dip” headlamps were made available as Bosch offered the first, two-filament bulb (incorporating both low and high beam functions). Dip switches to control high and low beam operations were typically located on the dashboard and it took until 1927, for the foot-operated dimmer switch to be widely used.
Light sources
To address the problem with rusting lighting reflectors, the sealed beam headlight was introduced in 1936. If the light burned out or was damaged, the entire non-repairable unit had to be replaced. Sealed beams used two filaments (one, for high and one, for low beam operation). In 1940 the U.S. government mandated the use of sealed-beam headlamps on all vehicles and, refused to change this requirement for more than 45 years, despite the continuous development of superior lighting technology, in Europe.
By 1950, cars were traveling at higher rates of speeds, posing a problem at night as headlight beams did not project far enough ahead, for safe driving. To address this issue, the asymmetrical beam was introduced where the lens of the headlight illuminated only the lane of the road that the vehicle was driving on. The resulting beam pattern was light focused lower, towards oncoming cars and higher, to the right of the road, projecting the light a greater distance.
Hella, a German company, introduced the halogen headlamp in 1962. Light efficiency was one and a half times greater than previous lighting and service life was doubled. Other benefits include, lower heat emission and the light could be made in a variety of shapes. Rectangular shaped headlamps were approved for use in the U.S. in 1974 and by 1979 the majority of new cars sold in the U.S. were equipped with either round or square halogen sealed beams.
HID (high-intensity discharge) headlamps were first used on the 1991 BMW 7 Series. HID lamps have no filaments but use a high-voltage arc, that emits light in an atmosphere of inert gas. HID metal halide lamps have been around for a while and are used to provide general lighting in parking lots and along highways. These lights have a long warm-up time and won’t work for automotive use. HID bulbs designed for cars are filled with xenon gas that reduces start-up time. To ignite the arc, a high starting voltage (18,000v to 30,000v) is required and, supplied by ballast and ignitor, that controls current sent to the bulb. Once the arc is operating it requires less, or the same amount of electrical energy as halogen type bulbs while providing more light. Another advantage is the longevity of HID bulbs that typically last around 2000 hours versus halogen bulbs that only last 450 to 1000 hours.
This reflector type of headlight from a 2014 Ford F-150 has complex multiple surfaces that create a designed light pattern on the road. A single, two-filament halogen bulb is used for low and high beam operation.
A recent innovation in automotive lighting is the light-emitting diode or LED. An LED light uses a semiconductor light source that emits light when current flows through it. LEDs are solid-state electronics with no components that wear out (like bulb filaments used in halogen lights or tungsten electrodes in HID bulbs). Unlike halogen lights that have an average service life of around 500 hours, LEDs can be used for around 8,000 hours. The use of LEDs as a light source saves money for consumers as LED replacement is no longer a maintenance cost. This is especially helpful on many late-model vehicles where replacing a headlight bulb requires disassembling the entire front of the car to gain access to the bulb.
In addition, LED illuminated headlights are 80% efficient in light production and only waste 20% of electrical energy to heat. Halogen lights invert this energy use as they waste 80% of their supplied electrical energy and only use 20% to produce light. Adding to their longevity and versatility, LEDs are highly resistant to vibration and can be used in physically smaller headlight assemblies.
In the U.S. the 1986 Chevrolet Corvette used the first LED in its center, high-mounted stop lamp. The first use of LEDs for headlights was in Europe, on the Audi R8 where low and high beams (along with parking lights and front turn signals), used LED light sources. 2009 was the first year that LEDs were used in headlights in the U.S. on the Lexus LX 600h. It featured LED low beams and side marker lamps. In the same year, the Cadillac Escalade Platinum used LEDs for the low and high beams, as well as for position and side marker lamps.
Introduced on the 2014 BMW i8 and Audi R8 LMX, lasers are one of the latest light source innovations for headlamps. In operation, three diodes project a blue-colored laser beam into a prism that focuses the three beams into one. The single-beam passes through a phosphorous lens that changes the blue light to white, where it bounces off a reflector, directing the beam onto the road. In 2018, the trend to miniaturization lighting components, resulted in deploying a much smaller laser module, powered by just one high power laser diode on the BMW8.
With nearly double, the projected lighting distance of LEDs (around 6,500 feet) and 30 percent more efficient, laser sourced headlights could be the future of automotive lighting technology. Laser diodes are ten times smaller than conventional LEDs and help to reduce weight and installation space inside a headlamp. Using a laser light source, the size of the reflector surface can be reduced by a factor of up to ten versus the same headlamp using LEDs.
Currently, laser headlights for BMW and Audi models add $8,000 to $12,000 to the price of the car. Even for these expensive cars, this is a rather pricey option so it will take time for laser headlight technology to be affordable on main-steam automobiles. In October 2018, the National Highway Traffic Safety Administration (NHTSA) issued a notice of proposed rulemaking that would allow for better headlights including laser technology. Don't expect to see laser headlights on U.S. roads for a few years as they will have to undergo testing to be approved, and it will take some time to fit them to U.S. production-spec vehicles.
Reflector vs. Projector
Reflector and projector are the two types of headlight housings used in the U.S. Reflectors used for automotive lighting have been in existence for more than 120 years. In operation, a light source is located near the focus of the reflector. The reflector bounces the light through a lens, where it is dispersed onto the road.
The pattern of light output is designed into the optics of the reflector instead of the lens. Many reflectors are a parabola that is U-shaped, symmetrical, and provides a basis for more complex shapes. Modern reflectors have many individual segments and complex contours. Each segment is designed so that its cumulative effect outputs the designed light distribution pattern. On newer headlamps, optics molded into the headlight lens refract, or shift some of the light sideways and vertically, further directing the light distribution pattern.
Reflectors that use a two-filament bulb operate as follows. Light from the low beam filament bounces off the reflector that directs it down onto the road. When the high beam filament is operating (low beam filament is off) the light source position is shifted causing light to bounce off different segments of the reflector’s surface, creating a light pattern that shines more upward. On some bulbs, a shield is used keeping light from the high beam filament from projecting towards sections of the reflector.
Commonly made of compression, or injection-molded plastic, modern reflectors use a surface where vapor-deposited aluminum provides a highly reflective surface. Extremely tight tolerances are maintained in the design and production of these complex-reflector headlights. The halogen light bulbs are also made to exacting tolerances, regarding where the filament or light source is placed. Aftermarket HID (and to a lesser extent LED bulb replacement) for lighting may not position the light source in the same location as stock bulbs and, this can cause variations in the light pattern and direction of light output. When aftermarket lighting kits are installed in a vehicle the lamps must be re-aimed to compensate for this variation.
The first projector type of headlights was used by Chrysler in 1969. Projector lights use a light source (bulb, HID, or LED) placed between a reflector and lens. The elliptical-shaped reflector surrounds the light source and focuses its light on a single point about an inch ahead of the light. A shield is located between the bulb and lens and the top edge of the shield provides the light beam cutoff. This concentrated light is then dispersed by a lens into a tight beam focused on the road. The tightly controlled light pattern of a projector beam headlight increases its range and brightness and reduces glare for oncoming vehicles. Modern condenser lenses incorporate optical features specifically designed to direct some light upward towards reflective overhead road signs.
In some applications, the shield can be lowered by a solenoid to provide high beam operation. This type of projector light is known as BiXenon (HID) or BiHalogen. If the cutoff shield is fixed in the light path, separate headlamps are required for high-beam operation.
Headlight controls
Auto-on headlights used to only be available on high-end cars but, that has changed and today they can be found on many vehicles regardless of price. One of the earliest types of automatic headlamp was the Twilight Sentinel, that was featured on Cadillac, Buick, and some Chrysler cars in 1964. In operation, auto headlight systems use a photoelectric sensor mounted on top of the dash or the windshield near the rearview mirror. With the light switch in the "auto" position and twilight conditions, the system turned on the headlights. On current systems, ambient light-sensitivity is usually fixed by the manufacturer but, some systems allow drivers to adjust when the lights come on. In most states, rain, snow or other weather conditions require that headlights be on while driving. It’s a mixed bag, whether a particular auto-on system will react appropriately to weather conditions and drivers might have to manually turn on their headlights.
Automatic, or auto-dim high-beams are different than auto-on headlights in that they switch from high to low beams when an oncoming, or vehicle in front of a car is detected. Some systems combine auto-on and auto-dimming into one control. The idea isn't new and has been around since the 1950s. General Motor’s Autronic Eye and GuideMatic are some early examples of the technology. Today, the auto high-beam function is driver-selectable where, the driver keeps the high-beam switch in the on position and activates a second control for the auto-dimming function. Mounted on, or near the rearview mirror, a forward-facing camera detects oncoming headlights, taillights as well as streetlights (or other illumination) that indicates high-beam operation is not required. When these lights are detected, the systems switch the high-beam headlights off, and back on again once the lights disappear from the camera’s view.
Some recent examples of this technology are Ford’s Auto High-Beam Headlamps that use a windshield-mounted camera to detect other vehicles. The high beams automatically turn on during night time hours, at speeds above 25 miles per hour and dim automatically when an oncoming vehicle is detected. This system is available on some 2020 Ford models. Chevy’s IntelliBeam is a similar system and is part of their Enhanced Driver Alert package, first available on 2016 Chevy Tahoe and other models. In Europe, selective high beam, or glare-free high beam designs are legal and can be accomplished either by swiveling the light source downward or in the case of an LED light source, switching off specific LED chips that create a gap in the light pattern to reduce glare.
The future of headlights
Imagine a headlight that could be used in high beam mode continually and, never have to be dimmed, no matter traffic conditions. The same headlight could also project images, text, and symbols onto the road's surface to warn drivers of upcoming hazards. This functionality would seem to describe something from a sci-fi movie but, is instead technology developed by Marelli Automotive Lighting. First introduced on the 2018 Mercedes-Benz Maybach S 560 4MATIC, their h-Digi® system marks the first time Digital Micro-mirror Device technology has been used in an automotive application.
One of the most significant features of the system is its ability to use light as a communication tool by projecting an image onto the roadway. High-definition (HD) image projections can include vehicle guidelines, weather warnings, speed limit changes, construction zone cautions, pedestrian and animal warnings. After input from on-board sensors and computer analysis of driving situations, images are automatically projected directly in front of the vehicle. The goal of the projections in the driver's line of sight is to inform and/or warn them without distraction. Studies have shown that roadway projections are faster and less distracting at conveying information to drivers than a heads-up windshield display.
The technology not only increases safety and comfort in human-driven vehicles, but it will also play a role in semi-autonomous and autonomous vehicle development. More robust image projection is possible when leveraging vehicle-to-infrastructure (V2I) technology, increasing the types of messages that can be conveyed, i.e., four-way stop ahead, crosswalk symbols, railroad crossing, and many others.
Another outstanding feature of the h-Digi headlight is its ability to eliminate glare for other drivers. Glare from headlights of oncoming vehicles causes significant driver stress and distraction at best, and temporary blindness at worst. The problem of glare is multiplied when high beams are used. Although high beams are a nuisance to other drivers, they are beneficial on narrow, curvy, and poorly lit highways, especially in rural areas where wildlife routinely leaps onto the road. According to NHTSA, glare is not often reported as a cause of accidents. However, hundreds of fatal nighttime crashes attribute glare as a contributing factor.
The h-Digi system solves the problem of glare by disabling light that would normally illuminate on-coming drivers or vehicles being followed in the same lane. This takes place in real-time, as the system tracks the movement of oncoming vehicles and places a moving shadow where the vehicle is on the roadway. The view from the vehicle with the h-Digi headlights is that the high-beam is on all the time lighting up the road, far ahead.
Inside the h-Digi headlight, the module is a microchip with 1.3 million micro-reflectors. With two headlights a vehicle would have a total of 2.6 million reflectors. On-board cameras and sensor systems detect other road users and, a computer evaluates the data in milliseconds, providing headlamp commands for the best possible adaption of light distribution and/or image projection, for all situations. Each of the micro-mirror elements is approximately 10-microns in size or 1/1,000,000 of a meter (.00004 inches). These small mirrors can be individually controlled by moving them back and forth between two positions, on or off. Each mirror’s flip-over movement generates a pixel of the projected light or image.
Micro-mirror switching frequencies of a few hundred Hertz (cycles per second) are used to modulate the 1.3 million pixels to project an image, light up the road, or even play a video. The visual matrix generated is uniformly illuminated by high-current LEDs and, projected onto the street within milliseconds, employing a multi-level lens system. With HD resolution and precision computer control (of more than a million beams of light), high-beams can be left on continuously as their light is selectively directed onto the road and, avoids oncoming vehicles. This creates completely new possibilities of dynamic light distribution during driving as well as the projection of text or graphics. In 2020, Automotive News named Marelli Automotive Lighting a PACE Award winner for their work on the h-Digi headlight. The PACE Awards honor superior innovation, technological advancement, and business performance among automotive suppliers.
Conclusion
Just as the latest driver-assist technology (like automatic braking, stay-in-lane, or pedestrian warning systems) use an array of cameras and sensors, future high-tech headlight systems use this same technology and will present a challenge for independent repair shops. In the future, replacing a headlight bulb will become a rare occurrence as these new systems will likely use LED, or laser technology having a service life lasting longer than a vehicle is on the road! Besides, the bulb as a separate replacement part will become a repair of the past and instead, bulb replacement will turn into a "lighting module" replacement.
Parking lot speed fender-benders that damage headlight components will still offer plenty of opportunities to service headlights. After bodywork, paint, and installation of a new headlight assembly are completed, instead of replacing a $20 bulb a new headlight module would be required that could cost thousands of dollars. Also, auto-leveling headlight systems, windshield-mounted cameras, lidar, radar, and other sensors will have to be calibrated and/or initialized, using a scan tool to communicate with the vehicle’s body control module (BCM), to enable headlamps to operate properly.
While cutting-edge headlamp technology like the Marelli Automotive Lighting h-Digi system is currently found only on high-end vehicles like the 2018 Mercedes-Benz Maybach, (a $170,000 car), Mercedes-Benz S-Class Fast Lane and Audi e-Tron. These systems will eventually trickle down to less expensive models. As new lighting technology proves that it truly offers superior lighting for drivers, reduces accidents and saves lives, it’s not far-fetched that in the future they could be mandated in some form, by the U.S. Department of Transportation, for all vehicles sold in the United States.
Smart headlights that track oncoming vehicles at night (creating moving shadows to eliminate glare and project warning images on the road), are just part of the never-ending technological innovations and, will affect independent repair shops and the technicians that work in them.
