Could you explain how the headlamp is directed, its scatter and the ability or style of light to pierce the dark? I drive on hill-and-dale county roads and have experienced many times "high-beams" that were not. The intensity of the light was not the problem, its focus was. The worst offenders being SUVs, which all seem to be directed improperly. – Martyn
The ability to shape plastic into elaborate forms relatively cheaply has allowed car companies to take a whole new look at headlights.
And after relying for years on a tungsten filament to provide light, we now have rare gaseous substances, aided by elaborate electronics bringing us a whole new level of lighting.
The sealed-beam headlight used from 1940 until the 1980s used a glass parabolic reflector to gather light created by the bulb and project it forward in a single beam where it was directed and shaped by the glass lenses through an intricate design etched into them. At the same time that rectangular sealed beams came into being on this side of the Atlantic, Europeans were working with the same unit but with replaceable bulbs.
This soon led to the development of brighter bulbs such as the halogen bulb. They used the same tungsten filament in use since 1940, but now in a sealed unit containing halogen gas. This resulted in a brighter, whiter light with little yellow coloration. In 1983, replaceable bulb lights were permitted in Canada and the United States and halogen bulbs started to proliferate.
In the early 1990s, lights underwent a major change as manufacturers discovered the properties of plastic, among them the ability to be moulded into any shape. Now, instead of relying on the lens to shape and direct light generated by the bulb, reflector technology came into use.
Through the use of computer-aided design and technology, plastic parabolic reflectors could not only gather the light, but shape and direct it without the use of a lens. The lens itself could thus become clear, giving designers free rein.
The next advance was the use of gaseous discharge light sources such as those called Xenon, also known as High Intensity Discharge or HID headlights. Instead of a glowing filament as the source of light, these use a gas discharge process and extremely strong voltages to create an arc, similar to the concept used to light streets and stadiums.
They produce immense light from a small source – a bulb the size of a peanut without the shell. But, as much as 20,000 volts is necessary to "kick start" them, or they would flicker like street lights do when first turned on before they get up to operating temperature. This and the 30 volts necessary to maintain the arc that keeps the gas alight are produced and controlled by a "little black box" containing the transformer, capacitors, current regulators and other electronics. This results in a brighter light of a different colour.
Xenon lighting provides approximately 45 per cent more light, while producing 25 per cent less glare. But the story does not end here. The latest development is the use of LED (Light Emitting Diodes), which require far less power and provide an even whiter light. Already popular for parking, turn signal and daytime running lights, they are coming into use as the main source of light. The 2014 Mercedes E-Class cars will use fixed LED lights for low-beams.
In all cases, the parabolic plastic reflector is the key to the light emitted from the front of a vehicle. Virtually all of these used by car manufacturers are produced under strict requirements. The problems lie with scratches or other damage to the lens through which that light is passing, improper use of high beams, poorly aimed headlights, improper positioning of lights (too high) and illegal lights (high-wattage bulbs in non-compliant, aftermarket installations).
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