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Like almost every other aspect of automotive technology, headlights and vehicle lighting have been undergoing both evolutionary and revolutionary changes in both design and function. The latest innovation that is now appearing on most new cars, trucks and SUVs is LED (Light Emitting Diode) headlamp systems. In 2019, 86% of new vehicles cam factory-equipped with LED headlamps.
LEDs are been around for many years, but were mostly used for indicator lamps, center rear mounted brake lights, turn signals, daytime running lights and styling bling to dress up the front of a vehicle. One of the limitations of those early generation LEDs was their relatively low light output compared to conventional headlamps. However, as LED technology evolved and improved over the years, it soon became possible to achieve the same or better light output as conventional headlamps. That opened the door for large scale adoption of LED headlamps by the auto makers.
In 2007, LED headlights were first used on the Lexus LS600h in the U.S. A few years later, Audi offered LED headlamps on the U.S. R8 models. As time went on, more and more auto makers began to offer LED headlamps. In 2014, Cadillac became the first U.S. auto maker to offer LED high and low beam headlights on their Escalade Platinum models.
In recent years,LED headlamps have been offered in various configurations, giving the auto makers much greater freedom in how they design their headlamp systems.
On the 2014 Cadillac Escalade, the LEDs are stacked in two rows within the headlight housing to mimic the styling of the rear taillights (which also use stacked LEDs). A total of seven LEDs are used in the headlights to stitch together the low and high beam patterns. Each LED is aimed at a different portion of the road in front of the vehicle, providing precise illumination exactly where it is needed. This projects a sharper more focused beam pattern than what is usually possible with conventional headlights or even HID headlights.
LEDs have a number of important advantages over conventional halogen headlights as well as HID (High Intensity Discharge) lighting systems. For one, LED headlamps are extremely long lived, lasting upwards of 25,000 to 50,0000 hours or more. On most applications, the LED headlamps will likely last the life of the vehicle because there is no filament to burn out or break as is the case with conventional incandescent and halogen bulbs. Also, there is no glass bulb to leak or fail as there is with incandescent and HID headlamps because LEDs are a solid state diode. Consequently, LED headlamps can handle severe vibrations and rough road conditions that might cause conventional incandescent or halogen headlamps to fail.
LEDs also offer improved lighting performance. The brilliant white light they produce is as good as or better than conventional halogen headlamps, with less glare than the bluish light generated by HID headlamps, which many oncoming drivers find to be very annoying.
LEDs are also extremely energy efficient compared to conventional incandescent and halogen headlights. and are nearly as efficient as HID lighting systems. The efficiency ratings in lumens per watt are as follows:
Conventional incandescent headlamps: 8 lumens/watt
Halogen headlamps: 25 lumens/watt
HID D2 headlamps: 90 lumens/watt
LED headlamps: 70 lumens/watt
The more efficient the headlamps, the less power they require. This reduces the load on the vehicle's charging system and battery, which improves fuel economy (and range in an Electric Vehicle). LED headlamps typically improve fuel economy about 60% compared to conventional and halogen headlamps!
Another difference between the light produced by LEDs and incandescent and halogen bulbs is that LEDs produce "cold" light that contains no infrared wavelengths that heat up things the light shines on. You can hold your hand in front of a LED headlamp and feel no heat unlike that from a conventional incandescent or halogen headlamp.
There is also no Ultraviolet (UV) light generated by LED headlamps, which means no annoying bluish glare like that produced by HID headlamps.
Although LED headlamps produce much less heat in the light producing element compared to incandescent and halogen bulbs, the electronics that regulate the voltage and current to the LED diode do produce a lot of heat, which must be dissipated by some type of heat sink behind the headlamp. The cooler the assembly runs, the longer the LED headlamps lasts. Extremely hot climates or operating environments can reduce the overall life of LED headlamps.
Another trend is recent years is the use of "Adaptive" lighting on some vehicles. Headlights that automatically switch from low beam to high beam to extend visibility have been around since the 1950s. Most use a light sensor to detect oncoming traffic and switch from high beam back to low as another vehicle approaches. But some cars are now using vehicle speed to switch the lights from low beam to high when the vehicle goes faster. And with some of the new LED headlight systems, the beam pattern can actually change as needed to reduce glare to oncoming drivers.
To prevent blinding oncoming drivers, low beams have a range that is limited to about 350 feet, with most of the light falling in an area about 60 to 200 feet ahead of the vehicle. The low beam pattern and range depends on the optics of the headlamp housing, how accurately the headlamps are aimed, and the wattage of the bulbs. But regardless of what type of headlights are used, at 40 to 50 mph the vehicle is traveling faster than most drivers can see with low beams alone.
On curvy, winding roads, high beams aren't much help because conventional headlights are aimed at a fixed position straight ahead. Consequently, a driver might not see what's around a curve because his lights are shining off the edge of the road. With adaptive lighting, inputs from the steering wheel sensor are used to "steer" the headlights as the vehicle turns. Some systems can rotate the headlights from 7 to 15 degrees right or left as needed to improve visibility on curvy roads. With LED headlights, switching pre-aimed beams on and off can also be used to shift the light pattern left or right as needed for better illumination.
In 2023, the National Highway Traffic Safety Administration (NHTSA) will issue new rules that should allow greater use of adaptive LED lighting on new vehicles sold in the U.S. market. Right now, some of the European and Asian adaptive lighting systems do not conform to current NHTSA rules and are not allowed in the U.S. market.
An LED is a solid state chip, comprised of two layers of silicon semiconductor material doped with various elements. When voltage is applied to the diode, the two layers interact and produce a surplus of electrons. The reaction produces photons of light which shine forth from the diode. A reflector behind the diode helps direct the light forward to concentrate the light.
LEDs are very sensitive to the amount of voltage and current that flows through them, so behind the light producing diode is electronic circuitry that regulates current and voltage to protect the diode and assure consistent light output. If the LED is overloaded with voltage, the diode can overheat, burn out and fail. Consequently, if an LED headlamp does fail it is likely due to a problem in the control electronics or wiring.
Although LEDs are very long lived, the intensity of their light output can slowly dim over time. This is due to degeneration of the silicon semiconductors in the diode.
Can you replace an older incandescent or halogen headlamp with an aftermarket LED headlamp? Yes. LED replacement lamps are available, but swapping an LED diode for a conventional bulb may or may not improve lighting performance.
Although the aftermarket LED lamp may be rated with a higher light output than the original conventional or halogen headlamps on your vehicle, the position of the lighting element inside the headlight housing affects how the light is reflected and projected on the road ahead.
The positioning of the bulb within the housing is critical because of the way it aligns with the reflectors in the lamp housing. If the light source is repositioned too far forward or rearward, it can really screw up the optics and change the light pattern drastically. Likewise, if most of the light from an LED lamp projects straight ahead rather than radiating outward in all directions like an incandescent bulb, it won't reflect and project the same as before. The beam pattern may be overly concentrated in a narrow area ahead of the vehicle rather than properly dispersed and focused across the entire road ahead.
A properly designed replacement LED headlamp will have the LED diodes mounted on the sides of the assembly to simulate the same light characteristics as the original incandescent halogen headlamp bulb it replaces.