The total headlight system is usually composed of multiple converters, each regulating a different part of the system. 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. More frequently, however, the low beams are implemented by one or two strings at full brightness, and the high-beam function combines the low-beam strings with another string or two at full intensity. That approach allows the manufacturer to use the additional strings to increase the beam spread of the high beam by mechanically positioning the lights facing an adjacent angle.
The LED-based headlight mainly includes two basic electronic components: the LED array and the lighting control unit (LCU). The LCU usually houses all the current regulators and other power converters, as well as the microprocessor, which communicates with other electronic control units (ECUs) throughout the automobile. Upstream, the body control unit (BCU) controls the LCU and manages all the body functions in the car. The LED array is located on a heavily heat-sinked assembly that contains the LEDs, thermistors for measuring temperature, and coding resistors, which are a simple, cost-effective way to program the LCU power output.
Future headlight systems
This system most likely will become even more complex as additional functionality is added to the headlight, including dynamic fading for cornering lights, dynamic anti-glare systems, and increased safety functionality. Current headlight systems already use camera input to run auto-leveling motors, which respond to changes in the position of the car relative to the terrain. These cameras can be used to control dynamic light output, as well.
From a power electronics point of view, it makes sense to use a two-stage topology for a dynamic front lighting system. In a DC link topology, for example, a boost converter takes the 12V battery input and provides a stable high-voltage DC rail. Then, independent buck converters can be used to drive each series LED string separately in the system. This boost plus buck system (see photo below) is inherently more efficient and provides better mitigation of electromagnetic interference than the single-stage buck-boost systems, since the input and output current are both continuous. Additionally, the buck converter is an excellent choice for regulating output current, due to its high output impedance, which makes it look like a true current source.
Future headlight systems will use two-stage power architectures.
The cascaded DC link approach has better dynamics, as well, since the first stage can ballast the input transients of the car battery to provide a well-regulated DC rail with significant energy storage capability, while the second stage can ensure consistent regulation at all times. It is also much easier to perform high-speed PWM dimming on a buck stage with little or no output capacitance, allowing for much more resolution and a higher contrast ratio when PWM dimming. This amounts to a higher level of controllability in the system, providing the possibility for dynamic fading of the different parts of the system.
Since the automotive market is not as cost-sensitive as consumer electronics, this move to two-stage LED headlight drivers could have staying power in the market due to performance improvement and additional safety functionality.
I am from Bangalore, India. I find you area still arguing from the point of beam dispersion, focusssing and how nice it looks form the point of the person behind the wheels of a vehicle fitted with HID lights. The roads in developed countries are well lit and vehicle owners need to drive with just parking lights or lights with low beam. May be when you are driving on highways may be you can use high beam headlights and that is when I am sure you will like these HID lights.
But if I am in a vehicle or a pedestrian crossing a badly lit city road and facing oncoming vehicle fitted with HID lights working at high beam – the experience is terrible. You get blinded for a short while. Kindly do come and walk down our roads. Our drivers use high beam within city limits. People show off HID lights by using high beam- least concerned with impact on others on the road. These lights should be banned- as our drivers do not show that much common sense.
Any light should not hurt (eye sight) of those facing the head lights. I still think automotive companies need to look for some other better alternative solution.
M S DIVEKAR, a properly installed and aimed HID headlight setup should not cause problems for other drivers.
But, one of my pet peeves, are when people install aftermarket HID bulbs in a non-projector assembly. When they put the HID bulb into thast type of headlight, the beam scatter is incredible and painful to view. Not only that, the light dispersion is so bad with that, it probably doesn't illuminate the road any better than their old headlamps. I frequently see this done in "import" cars, and they usually choose some 8000k + color, making it an annoying blue or purple color.
The lights that I installed have a nice, focused beam, and a crisp cut-off line on low beam (actually a mechanical shutter). I also took the time to aim them properly, to avoid irritating the eyes of other drivers.
You have only stated how much you benefitted when HID lights were fitted on your mobike. You must know how much the same HID lights hurt the eyes of the driver of the on-comming vehicle or pedestrians trying to cross a road- looking into your head lights. Peopel looking at tehse lights - get blinded for a sort time and taht could result in accidents. That is why these lights have been banned in some countries, but powerful lobby of manufacturers also know how to beat the law enforcers- asking them to look the otherway round. Same applies to LEDs too if fitted as head lights at any time in future.
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.
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.
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.
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.
@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.
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...
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.
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