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Old 02-20-2008, 01:42 PM
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Tekknikal Tekknikal is offline
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Default Car Tech: Lighting

The StreetSeen Technical Series is back! In our last article I gave a primer on braking systems. This time, we talk about lighting.

To the layman on the street, the topic of lighting can be quite boring. What could possibly be involved? It's important to enthusiasts though, and in reality, setting up a proper system requires a decent understanding of the physics involved. Recently, we've seen some lighting systems that are just sexy. When you see a Vitara, TSX, or S2000 coming at you with flickering purple-red-blue-green headlights you know what I mean.

Lighting is a critically important aspect of a car. While it's required by federal law safety reasons, it's also modified by enthusiasts for improved aesthetics and performance. Today I'll be talking about lighting systems, from headlights to tail lights and sidelights. I'll go over what makes one lighting system better than another, with the goal of helping you to be able to evaluate lighting systems for yourself. Continue reading for the breakdown on automotive lighting.

How Light is Created

Basics: The Filament

Let's start with the basics: the typical light bulb. Technically, they're call incandescent lights. They're used all over. Most of you are familiar with how these lights work. There's a really thin filament inside of a bulb that contains a special gas. When you pass current through the filament, it gets hot and begins to glow, starting in invisible infra-red (this is called incandescence). Now, ordinarily, that filament would melt or catch fire, but a combination of special filament materials and gases used inside the bulb prevent that. Anyway, as you apply current, you will get the filament hotter. Eventually (less than a second in modern light bulbs) it will glow, and that glow will become bright enough to see. A lot of the light is actually Infra Red, which you cannot see and is felt as heat. As you add more current though, more light gets emitted in the visible spectrum. This is light you can see. As you could imagine, this is inefficient because most of the energy used becomes heat. You really want the energy that you use to go into what you want: light.

Regardless, this age old technology works well, and is used in pretty much every part of the car today. Recently however, we've seen the emergence of two additional technologies in automotive lighting: LED lights and Xenon based lights. I'll now explain how each works.


LED lights work by pushing current across a tiny device called a diode. This is what gives them their name- Light Emitting Diode. Think of a diode as a simple material that can conduct electricity. It was discovered that diodes constructed from very special (but not necessarily rare) materials have the ability to create light at a specific wavelength ie a specific color (with white being achieved via a special coating on blue). While the light that's created is the result of a flow of current, it is not created from incandescence. That is to say, it doesn't take heat to make light like filament light bulbs.

This means a number of things: because light is created at a certain wavelength, the color of the light is perfectly fixed and controlled. Also, because you don't need to get a filament hot, there's less wasted energy and LEDs run cooler and more efficiently. Another advantage is speed: LEDs can generate light faster than traditional light bulbs because they don't have to be heated first. Yet another advantage- and this one major- is that LEDs are more reliable. This is because they are much less fragile and the process of creating light is less abusive.

On the flip side, LEDs require carefully controlled environments in order for them to be created. Also, while the materials required to make them are not rare, the machinery is expensive. In addition, it requires a great level of engineering to be able to create an LED that will flow large amounts of current to create a lot of light. Then once that light is created, the LED must be cooled because of the large current flow in such a small area. Note that this only applies to cases where very large amounts of light need to be created.


You can think of Xenon lights as being similar to normal / filament based lights, except that instead of heating a filament to create light, a plasma discharge creates light. How does this work? Allow me to explain.

It all happens in a small chamber which we'll called a quartz arc chamber. This chamber contains two electrodes on each side (think of them as prongs penetrating into opposite sides of the chamber). When you apply a voltage to these electrodes, a spark is created as the current leaps (arcs) through the bulb as it goes from one electrode to the other (remember the electrodes are very close as the chamber is very small).

This tiny quartz arc chamber contains a special gas- xenon gas, as well as mercury and special salts (in this example, sodium). The xenon gas provides a safe and stable environment for the spark (actually a plasma discharge) to travel through. It also helps the entire process to happen quickly, allowing light to be generated very shortly after current is applied.

Sodium inside the chamber melts as it hits the plasma discharge. This creates a great deal of visible light and also determines the color of the light produced. Mercury inside the chamber helps maintain voltage and pressure, which helps stabilize conditions inside the chamber.

Stadium lights use a similar technology. And if you've played a sport in a park at night, you'll know it takes time for the stadium lights to turn on and get to full brightness. So ordinarily, it would take a lot of time to get useful light from this system. Not good if you just want to drive up the road, right? On top of that though, you'd find it hard to safely keep the light on- it's picky about the voltage and current it requires.

The Ballast is the unit that solves these problems. The ballast controls the startup of the light bulb and maintains the light once started. Chemicals inside the quartz arc chamber help ensure you get light almost instantly.

All of that is technical but explains things you may have noticed about xenon lights. For instance, right when someone turns on their xenon lights, you may notice the color is very blue, before it slowly changes color to a more stable, more whitish (or more 'warm') color. You will also note that the light slowly gets brighter as it 'warms up'.

This is because when you start the light, the ballast provides a very large ignition pulse to get the light creation started. After this, the different chemicals start to burn at different times, changing the color from blue to yellowish white to the final whitish color (assuming that's the target color). All the while, the ballast is taking 9-16volts DC power and is regulating it and scaling it up to meet the requirements of the bulb.

The benefits of Xenon are many. First, a great deal of light can be created with a much greater efficiency than normal filament based light. This means less heat is generated. Second, the light can be created in a more carefully controlled color such as white. Third, less energy is required to make the light. This means that if you have a high current sound system that's taxing your car, your xenon headlights would be less likely to dim.

How Light is Used

Today nearly all cars on the road use either filament based tail lights or LED tail lights.

Tail lights that use filaments tend to have very few bulbs. These bulbs are often red in color, if the tail light itself isn't red. The light they generate is reflected inside of the tail light, illuminating the entire assembly red. Tail lights that use LEDs tend to use a number of small LEDs that naturally glow red. The difference is obvious when you see them: you can see the tiny LEDs illuminating in LED tail lights.

The same holds true for signal lights and side indicator lights.

Most headlights today are made from either filament based lights or Xenon lights. With the headlights off, you would not normally be able to tell which is used, unless you looked at the housing labeling.

But what about the headlights that look like lenses you ask? Those lights, called projectors, can be used with either traditional filament lights OR xenon lights.

Projector lights

Once you create light, you must somehow control how this light gets out to the world. Sometimes you want to light yourself up, other times you want to light something else up. In cases you want to light yourself up, you might use reflective materials inside of the light assembly. This is how traditional tail lights work. But if you want to light something else up, you need to shape the light that gets created. You need to create a beam pattern.

Beam patterns are important because you only have a limited amount of light, so you want to put it all on the road. In addition, you don't want to blind everyone else on the road. To create a beam pattern, manufacturers shape reflective materials in a certain way to aim the light where it needs to go. The US Department of Transportation mandates how the light should look going forward (called cutoff). This policy makes sure that your light is being used effectively and safely. In different parts of the world, different regulatory agencies require different cutoffs. This is of particular note to us here in the Virgin Islands because we drive on the left side of the road- while our headlights are setup to be used on the right side of the road. The consequence of this is that our right headlight is more likely to blind someone than it should be. So, when it appears that someone has their high beams on, they might not really have their high beams on after all. It may be that their headlights need adjusting and/or their cutoff is too high.

Projector lights are a step up from reflectors in that they use a lens to focus light onto the road. This results in a much more efficient and even light output. You will notice this as the cutoff lines for projectors tend to be very sharp. The design of the projector also controls the color of the flicker that you see when an appropriately equipped car drives towards you (many cars do it including TSX, S2000, TL, Maximas, Porsches, Vitaras do this). When the projector is focusing its light, some parts of the light get bent and scattered at the cutoff. This is why the light appears to flicker and sparkle in different colors when its coming at you (you're looking at the top of the car's cutoff). This is also why the actual light they put down on the road is not colored. Because this effect depends on the projector assembly itself, some cars with projectors will not show this effect at all, while others are more pronounced. Also, because this is a property of the projector, you cannot duplicate the effect by using HIDs or other lights of a different color.

(note that this example shows a number of desired traits including a sharp cutoff line as well as a colorful cutoff. someone looking at the light (lowbeam pictured) from above the cutoff will not be blinded. at the cutoff the headlights will flicker in the colors you see in that cutoff band. below the cutoff and you will be staring at a very bright light! also note that the right side is angled higher. this is setup so that when the pictured car is driving on the right side of the road, incoming cars on the left are not blinded while the driver is still able to see what may be happening off the road to the right. source: nasioc)

Some of the different types of projectors are visible to you just by looking at them. After 2006, TSXs and other cars were required to change their headlight designs because some complained about the flicker the vehicles had. As a result, a new type of lens was used. You can see this lens as it looks like it has concentric rings on it. These lenses are called Fresnel lenses, and in the case of the TSX, replaced the original clear lens. The flicker- which was created when light hit the step of the cutoff and broke in a prism like effect- was then minimized. Some enthusiasts modify their lights however, swapping their Fresnel lenses back for clear lenses, and modify the shield slightly (called colormodding) to get back the colorful flicker in blue/purple and even red.

More on Color

In the past, if you wanted to change the color of your light, the only way you could really do it was by putting a colored filter over your light bulb. The problem with this is that it lowers the total amount of light you put out by eliminating all the colors but the color of the filter.

Xenon and LED lights are different however. LEDs are manufactured to output in certain colors, and a wide variety are available with some being more expensive than others. Similarly Xenon bulbs are manufactured to output different colors, but typically only within a certain scale, called color temperature. The temperature of the light is described by a number of Kelvin, where sunlight tends to be about 5,000K on a bright and warm sunny day. See this scale for an idea of how the color temperature scale works:

(image source: wikipedia)

1700K Match flame
1850K Candle
2800K Tungsten filament lamp
3200K Sunlight/Sunset
4100K Moonlight (its not as blue/white as you'd think because we see colors differently at night)
5000K Typical warm daylight
5500K Typical cool daylight/ electronic flash
6500K White on a properly calibrated RGB Monitor
7000K Typical overcast sky
9000K blue sky (goes as high as 12000K)

Most OEM headlights come in the 4300K-4700K range. Yes, even those that flicker blue. Remember, that flicker is caused by the projector and is only visible at the cutoff line. When you look at the light on the ground, it is much closer to yellowish-white. Its whiteness is very pronounced though, because normal headlights are at a lower color temperature.

In general, Xenon lights are brightest when they are manufactured to output in the 4300-5500K range. Beyond that, and you actually get less light. By 6000K, your light has been reduced by 10-20% depending on the quality of the bulb. By just 7000K - 8000K you will have lost between a quarter and half the light output possible. Note that while the light will appear bright because your eyes are more sensitive to white, the 'real' drop in light outweighs this by 6000K. In general, colored xenon light will still continue to be unusually bright compared to normal light bulbs because normal bulbs would require filters. Again though, by utilizing a higher color temperature beyond 5500K, you're limiting the light output you could otherwise have with Xenon, in exchange for a more bluish looking light.

As Xenon lights get older, their color temperature rises ever so slightly- a phenomenon called colorshifting. A brand new OEM light at 4700K for instance, may get as high as 5500K through its life. They will also get slightly dimmer and lose about 10-20% of their initial brightness. Although they will continue to be much brighter than traditional lights and this decline is essentially not noticeable, it is a bad idea to flash HID lights on and off too often as this reduces bulb life.

There are a couple ways high beams are handled with Xenon systems. The first is to utilize a separate reflector for high beam use. This reflector is a non-xenon traditional light. The second method is commonly called bixenon. This design typically consists of a projector based xenon system that contains a movable shield. While low beams are being used, the shield is down, keeping light on the road only. When high beams are requested, a solenoid (really just a magnet controlled by current) moves the shield downward, which allows more light out and up. Sound backwards? It is. When the light is passed through the lens, it is flipped upside down and backwards. Since the cutoff is the point where the shield allows light to escape, when it goes downward, more light escapes down into the lens, and since the lens flips the light, the escaping light goes higher to the outside world.

The Future

Looking down the road, there are a couple key technologies emerging that will impact lighting on cars. As LEDs continue to become more advanced, car headlights will continue to evolve. Already we are seeing adaptive technologies where headlights are mounted gimbals that allow them to turn with the car, allowing the driver to see further into curves or higher up a hill.

One notable such headlight design is featured in the new Nissan GT-R where the car has a fixed projector as well as secondary xenon reflectors that are mounted such that they can widen the beam pattern as needed. In this case, high beams are handled via a secondary non-xenon reflector unit.

Another development has been adaptive headlines. The concept here is simple: the headlight projector itself moves to "see" into turns or up hills. Cars with these systems have sensors in them that tell the computer the angle of the steering wheel and the angle of the car. If it sees the driver turning or feels the car is climbing or descending a hill, the computer will adjust the beam accordingly. The following diagram illustrates the system components:

And the benefits:

Yet another new development is the use of LEDs in headlight applications. As of today only three cars feature LED headlights: the Lexus LS600, the Audi R8 (as an option), and the Cadillac Escalade Platinum Edition. LED headlights offer the benefits of using relatively little energy to run and can be made to fit a wide variety of packaging constraints- allowing designers more freedom in designing the front ends of cars. On the flip side, current LED headlights offer less output vs most HID systems at 2000 lumens vs the 3000 lumen average output from an HID system.


To conclude, getting good light on the road is nowhere near as simple as putting hyperwhite bulbs in your headlights. Also, you don't want to just shine high beams everywhere. Ideally you want to maximize your light output and optimize its delivery. On today's cars, that leads you to either Xenon or LED based projector headlights, with LED signal/indicator lights elsewhere. In addition, getting light that meets your requirements and tastes may force you to make compromises depending on what you're after.

Special thanks to Paul Lin of IGTAutomotive for his editing assistance with this article.
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Old 02-20-2008, 06:21 PM
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Default Re: Car Tech: Lighting

great read...good job...!
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Old 02-22-2008, 09:27 AM
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