Better and brighter: Headlights go high-tech

Last weekend's time change accelerated the onset of dusk, which means you're soon likely to be driving in darkness to or from work, or both, if you're not doing so already.

Fortunately, headlights in today's cars and trucks are more advanced and efficient than ever before.

In fact, few vehicle components have evolved as dramatically from their origins as the headlight.From the earliest mirror-reflected candles and kerosene lamps, through tungsten bulbs and glass reflectors to sealed beams and today's exotic HID and LED technology, headlights have been constantly improving.

With that evolution has come variety, which means that there are now substantial differences among vehicles in their abilities to light up the road ahead ? differences that may affect your satisfaction with a particular vehicle, depending on your driving regimen.

It's not that long ago that there was little difference at all among headlights. From 1940 until the early 1980s, only sealed-beam headlights were permitted in new vehicles sold in North America ? although the permitted size and shape of those lights expanded over the decades to encompass both large and small round and rectangular forms.

Sealed beams combined the reflector, lens and filament(s) in a sealed unit. All relied on tungsten filaments in a vacuum, like those in conventional household bulbs, to emit light when they were heated by electricity passing through them.

The first major change to that formula came in 1978 when halogen-sealed beams were first permitted in North America. They continued to use tungsten filaments, but only in the presence of a halogen gas that enabled them to burn brighter without diminishing their life.

The term halogen encompasses several inert gases so halogen bulbs were also sometimes called quartz, quartz-iodine or iodine.

A bigger change came in 1983, when composite lights became legal here ? lights with separate bulbs, lenses and reflectors.

Following that change, replaceable halogen bulbs gradually became the norm, as did molded plastic lenses ? although those lenses retained an integral role in determining the light's distribution pattern.

During the next decade, engineers learned to design sophisticated plastic reflectors that could direct the light beams in different patterns than the simple parabolic reflectors used until then. The design freedom that resulted can be seen in the styling of today's vehicles.

The ultimate expression of these polyellipsoidal lights, as they are known, is the projector headlight, which is small in diameter but very deep, with a condenser lens at the front and a shade between the reflector and lens to define the low-beam cutoff.

The shade can be moved electrically to vary the pattern between low and high beam.

Over the same period, gaseous discharge light sources were introduced. They're typically known by the terms Xenon or High Intensity Discharge (HID) headlights.

Instead of relying on a glowing filament for their light source, they employ an electric arc between two tungsten terminals to produce the light. The intensity of the arc comes from metallic salts that are discharged and vapourized within the arc chamber.

These lamps produce more light for a given level of power consumption than ordinary tungsten and tungsten-halogen bulbs. For that reason, they can be much smaller than a typical halogen bulb to achieve a desired output.

The use of xenon gas allows the lamps to power up almost immediately, unlike similar metal-halide lamps typically used for street and parking lot lights. The light from HID headlights has a distinct bluish tint.

The most recent development is LED (Light Emitting Diode) headlights, which provide a whiter light but require less power. Their small individual size and ability to be combined in a broad range of shapes give designers a newfound freedom in front-end styling.

Several 2014 models offer LED headlights and almost all now use LEDs in tail-lamps, as well as Daytime Running Lights.

As a result of all this diversity, your choice of headlights is almost as great as that of vehicles themselves.

Because there can be very real differences in the amount and shape of the light beam cast by these different systems, it's a good idea to test drive any new vehicle you are considering at night, under the conditions you will typically encounter, before signing on the dotted line.

You may be surprised at what you see.

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