Enlightenment – Modern Headlight Technology
When cars were first invented, much of the technology used in their design and use was carried over from carriages. Driving at night was done much in the same manner as the horse-drawn carriage- by candlelight. Carriages often had hanging lanterns with an oil lamp inside them, lighting the road. These quickly gave way to electric lights that replaced the oil lamp. Soon came glass reflectors in the back of the lantern, which was now solid-mounted. The evolution of the headlight was slow. The halogen bulb was invented in 1882, but its use in the automobile did not come until 1962. The typical sealed beam headlamp, the most common design, was first used in 1940 until the early 1990s, when the last of the sealed beam housings were phased out.
The modern headlamp is comprised of several styles and technologies, each with their own advantages and disadvantages. The main types of headlamp technology today are replaceable gas-charged bulbs, and HID or High-Intensity Discharge systems. This may seem simple at first, but it is far from it.
The gas-charged bulb is a development that comes from the halogen design. The first vehicle designed with replaceable bulbs since 1939 was the 1984 Lincoln Mark VII. This used a basic headlamp housing and allowed the owner to replace just the bulb, rather than the entire housing. Ford had to petition the US Congress to make changes to the US standards on headlights in order to build a car with these new replaceable bulbs. Before 1984, all headlights had to follow the standard designs allowed by Congress. After 1984, headlights could be different shapes, using the a standardized bulb.
Having the ability to change only the bulb helped foster technology development in headlamps. Through the use of different metals and gases, varied headlamp brightness and color is achieved. Tungsten was the original filament for electric headlights, and is still used to this day, however, in the early days; the tungsten was simply installed into the bulb in a vacuum, or inert gas and sealed. As tungsten burns, it boils off material, which condenses on the bulb itself. This eventually reduces the output of the bulb. This was not an issue with the large sealed beam units, but when the smaller bulb-only designs deteriorate quickly. Combine the short life with the low efficiency, the industry needed a change.
Combining tungsten with halogen allowed the bulbs to glow brighter with less current draw while retaining a longer lifespan over pure tungsten. This became the standard for all headlight bulbs. The European standards for headlamps were greater than that in the U.S., meaning European bulbs are allowed to be brighter. European tungsten-halogen bulbs were not made legal in the U.S. until 1993, with the H1 and H3 bulb designs, which are still available. In the U.S., halogen bulbs are allowed to measure 150,000 candela, which is double the output of a non-halogen sealed beam which is regulated to just 75,000 candela.
The first dual-filament bulb, the H4, came out in 1971 and allows for a single bulb to produce both the high and low beam in one housing. This bulb is commonly sealed-beam conversions in older vehicles. Halogen-type bulbs have a lifecycle of 450-1000 hours.
There are several different gases that are used inside tungsten bulbs. Halogen bulbs produce a yellow glow, this is the nature of the tungsten burning. As the tungsten burns, it releases ions into the bulb, which was discussed earlier. The addition of the halogen gas, either iodine or bromine, collects these ions and redeposits them back onto the tungsten filament. This eliminates the blackening of the bulb and prolongs the life of the tungsten.
Xenon is the other type of gas that is used in sealed bulbs. It is not a halogen gas, rather a noble gas, meaning it is odorless and colorless. Xenon functions in the same manner as the halogen gases, but when it is excited by electricity, it produces a bright white light. These are the lights that make you wonder if the guy heading towards you has his brights on. The result is a larger swath of lit road that extends further past the capabilities of halogen bulbs.
Xenon bulbs are also more efficient. Because the gas itself glows (as opposed to just the tungsten in halogen-filled bulbs), they are brighter and use less energy to shine. Xenon bulbs can last over 10,000 hours, so their extra cost is worth it in the long run.
Care in handling
One caveat for all bulbs is that the nature of the design makes them fragile. You cannot handle a halogen or xenon bulb with your bare hands. The oils from your skin will cause a hot spot, leading to failure, the glass will burst. Always wear gloves and NEVER touch the glass bulb itself.
High-intensity Discharge(HID) lighting has gained popularity in automobile use, but they have been around for a century. They were first used in U.S. cars in 1993 with the BMW 7-series. These lights use a high-voltage ballast that converts the 12-volts DC to 85 volts AC or 42 volts AC depending on the design. The bulbs are ignited like the fuel in an engine with a spark. This excites the Xenon gas that burns the tungsten electrodes. This is essentially an electrical gas bridge between the electrodes, replacing the hard-wired tungsten filament in a standard bulb. Once the light is sparked, the electrodes burn off ions into vapor, which then flows through the arc, creating an extremely bright light. This is the same process that is employed in street lights and stadium lights. HID automotive lights are Xenon-Arc type, where other HID systems are Metal-Halide, Sodium-vapor, and Mercury-vapor.
HIDs are designated with a D followed by the type and then the shield type. There are several types- D1S, D1R, D2S, D2R, D3S, D3R, D4S, D4R. Types 1 and 2 are 85 volts, 3 and 4 are 42 volts. S-type shields are used in projector lamps, R-type shields are for reflector systems. All HID lights give off significant UV light, but the glass lens absorbs all of it.
Projector beams use a magnifier to widen the beam. These are typically the low-beams, and they have a shelf limiter that stops all light from shining above a specific line. This is a safety feature as unshielded projector lights are too bright for other drivers. Reflector beams are used for low and high-beam lights. In these systems, the lamp shines onto a reflector which directs the light out the front of the vehicle, much like a halogen bulb.
HID lights shine with a color of 4100k or 5000K (white light), where tungsten-halogens are 3000k-3550k (yellow light). For reference, photographers use 5500k lighting for studio work because that is the color of the sun. HIDs are closer to sunlight, which makes them better for clarity at night. The typical HID light lasts about 2000 hours, roughly double that of the tungsten-halogen bulb. The tungsten-Xenon bulbs still last longer.
Some of the disadvantages of HID lights are the glare they produce and the cost. Replacing the bulbs, ballasts and ignitor components can be significantly more than the halogen-type bulbs. Converting to HID is very tricky. There are legalities involved and the only way to do it right is to replace the entire headlamp assembly and build a custom one. Budget HID conversions are not true HID systems and can cause fires. Be aware.
There are two new technologies that are emerging in the lighting industry – LED and laser. There are several models on the market today that use LED headlamps, including Lexus, Audi, and Cadillac. BMW has been playing with laser-powered headlights for their electric i8, but Audi beat them to the market with the R8 released summer 2014. Laser headlights have the ability to produce 70% more light per watt than LEDs, which is to say that they are beyond extremely efficient. The laser energizes a phosphorescent material which then glows bright white. The Audi Laser headlight system is supplemented by LED high beams.
Just when you thought all there was to headlights was pulling the knob on the dash. Headlight technology has been the same for 60 years, with very few changes, until the last 10 years, when modern headlight technology finally broke through the dark clouds like a ray of sunshine.
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