The automotive lighting industry has undergone a massive transformation with the growing trend toward LED-based light sources. As recently as 1990, the standard headlight assembly used only incandescent sources with very basic functionality: low beam, high beam, and off. Other functionalities, such as the turn signal, sidemarker, and position lights, were performed by separate incandescent sources. More advanced functions, such as separate cornering lights, race lights, and lighting features for advanced driver assistance systems, were not common or didn't even exist.
In 1991, the first high-intensity discharge (HID) xenon-based headlight was introduced, shifting the front lighting landscape into the power electronics realm. This shift to HID-based fixtures yielded a more efficient and longer-lasting system than its incandescent counterpart. However, HID lamps were far more complicated than incandescent sources, as they required extensive power electronics to operate. Like fluorescent lighting, HID lamps needed an ignitor to ionize the xenon gas, creating a conductive path through the lamp. Then a ballast comprising one or more switch-mode power conversion stages was required to regulate the lumen output in steady state. Unfortunately, this increase in complexity yielded little benefit in size or performance over the incandescent light.
Today's headlight systems typically use a single-stage power architecture.
In 2007, the first light-emitting diode (LED)-based headlights became available in new automobiles. LED-based systems also require some method of power conversion. An LED driver is required to convert the battery voltage source into a constant current drive for a series or series/parallel string of LEDs. While the LED driver also adds cost and complexity to the headlight system compared to incandescent sources, there are many benefits to the LED system, including size reduction, much higher controllability of intensity and color, efficiency improvement, and longer lifetimes. Over the past five years, it has become increasingly evident that the LED headlight should eventually dominate the automotive marketplace due to its inherent advantages over other light sources.
Existing front lighting systems
Today, LED-based automotive headlights typically are designed with single-stage power converters that take the available input battery supply of 12V and convert it to a regulated constant current output. This single-stage design usually requires a buck-boost topology of some type in order to provide regulation during load-dump and cold-crank conditions. Load-dump is when the battery or some other significant load is disconnected from the alternator during charging. During load-dump, the remaining connected automotive systems can see voltages of more than 60V for hundreds of milliseconds. Cold-crank refers to starting the engine at 0C when the battery can droop as low as 4.5V -- and in some cases lower. The buck-boost topology allows for the input to rise above or drop below the output voltage of the LED array while maintaining regulation. Converters that can buck or boost can be implemented in many ways, but some common configurations are the floating buck-boost (or boost to battery), the SEPIC converter, the flyback converter, and the Cuk converter.
The idea of being able to control the output of the light to such a degree is going to prove very useful to the automotive industry. I wonder what other industries might be able to take advantage of this flexibility.
I do marvel at contemporary automobiles. As one who works with microcontroller devices in many types of applications, it is no supprise that the lights mentioned here use a microcontroller to control functionality. Whatius really interesting is that the lighting microcontroller talks to the body control microcontroller.
This is just one step to an optimal lighting architecture that is automated. I can remember the days when I put driving lights (with a 1 mile range) on my Austin Healey. I had to be careful of where I used them, but no longer. Just program the LED lights and they will sense the on-coming traffic.
naperlou, Based on the amount of heat being dissipated by the LCU/LEDs, it makes sense to remove the headlamp driver function from the Body Control Module (BCM). The LCU will be control by the BCM through CAN (Control Area Network) communications.
James, now a day's most of the incandescent and traditional illuminant lamps are getting replacing either by CFL or LED bulbs. When we look in energy saving angle LED lamps are the preferable one, but its little bit expensive when compare with CFL. I think in coming days, when mass production happens, the cost may come down further. In future, it may replace all the existing lighting sytem across all sections like automobile domain, street lights etc
I recently replaced the landing light in my Cessna with an LED lamp. The original landing light pulled 20A and the lifetime was maybe 50 hours. Between the vibration in cowl mounted lights and the engine heat, incandescents just don't last long. In fact, every rental I ever used the landing light in burned out or would trip the breaker after 5 minutes. The LED replacement pulls about 2A and is rated for thousands of hours. With the lowered current draw and increased reliability I have the landing light on anytime the aircraft is moving. The FAA has approved LED replacements for most lighting systems. Even though there are no single bulb replacements for some navigation lights that have reflective surfaces inside the bulb, you can replace the entire light as a system.
I have to disagree with this part of this article:
"Unfortunately, this increase in complexity yielded little benefit in size or performance over the incandescent light."
Have they ever driven a vehicle equipped with HID lighting?
I converted my motorcycle from a dual halogen setup (H4 / H7) to dual "bi-xenon" HID projectors (4500k). Holy cow! It is almost a life changing experience to ride at night with the lights on high beam! :)
The performance difference in light output is incredible and I don't see how that can be denied.
That said, I'd love to install LED headlights on a vehicle...
@Jim- Just FYI the Ducati Panagale uses LEDs instead of HID or halogen headlamps. That will undoubtedly migrate downward into "everyday" bikes. There will be a significant safety benefit when tail lights go LED...as you know, incadescent brake lights fail often due to vibration. Often enough that most bikes have two bulbs in the tail light assembly.
I'm also surprised that car styling doesn't take advantage of the flexibility that LED's allow. Most LED-equipped cars just put them behind the classic round or rectangular shape.
The author writes "Sometimes the high-beam and low-beam functions are combined into one string. In this case, the high beam is implemented when all LEDs in that string are fully on. The low beam is implemented by pulse-width modulation (PWM), dimming the LEDs in the string to provide a lower-lumen output."
What a crock! Any lighting engineer worth his salt knows that the difference between high and low beam in a car is not simply more or less light, there is a legal requirement to ensure beam shape. For low beam the beam is supposed to reach virtually zero at ~100m by throwing the beam down. This is achieved (with incandescents) with a structure of baffles, the reflector and the position of the filament relative to the reflector. High beam on the other hand is a more open beam that throws much further. In the earlier days the power distribution was 50W for low beam and 55W for high beam, but the bulk of the lighting distance came from the beam difference. Basically according to this authors understanding of vehicle lighting low beam is allowed to shine in through the rear window of the car in front. I tell you it is not.
Kenish, the other more important aspect is LED requires a small amount of power to produce high intensity light beam, when compare with the HID or Halogen lamps. This will help to avoid battery drainage and hence save a considerable mount of power. If the rear and parking lamps are also replacing by LED, then power usage will be more and complete battery power drainage on overnight parking.
It will be a real benefit for drivers if the new LED headlights are mandated to not be as blinding as the HID lights are. IT appears that most of them are used primarily to blind oncoming drivers in city driving.
Presently the LED portion of vehicle headlamp assemblies appears to be an attempt at "styling" more than providing a useful amount of illumination. At least that is the way it looks to me when I see one oncoming. OF course, for those who drive an expensive car, I am certain that it is important to them that everybody else know that they are driving an expensive vehicle.
Probably it will be possible to produce some very useful arrangements of LED lighting on the vehicle, and certainly the best implementations will have the electronics for each light assembly in a separate module, both for heat dissipation and to reduce the cost of replacements, since automotive electronic assemblies do fail on occasion. REplacing a $750 dollar vehicle control module because one light's driver has failed would turn me against a brand of autos for a very long time. It would be good for the auto makers to realize that, and for some brand to take advantage of the lower price of single function modules.
Absolutely, William K. One would think that with the new computer controlled technologies and the ability to hyper-focus these lights, we should be able to address the issue of the oncoming driver (or walker, or biker,....).
Now, do these lights have some integral heater in them? As a Wisconsinite, I've driven in my share of snowstorms in which the headlights were the only thing in front not caked in snow because they produced enough heat to keep it melted. The issue isn't so much that I can't see (if that were the case, I would know enough to pull over and clean them off), but that other drivers can't see me at a reasonable distance.
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