The loss of a headlight makes nighttime driving hazardous, and may even attract the attention of the local police. A burned out taillight, stoplight or turn indicator lamp creates a hazard for other motorists because these lamps signal a vehicle's directional intentions to others. Bulbs that provide illumination for instrumentation are important because they allow the driver to monitor the speedometer and other gauges. Even something as simple as a failed trunk or dome light can create an inconvenience when operating a vehicle after dark.

SEEING THE LIGHT
Years ago, all headlamps were sealed beams. So if a vehicle needed a replacement headlamp for a 1980s vintage or older vehicle, there were only a few basic sizes of round and rectangular beams: those for two headlight applications (6014 round hi/low sealed beam and 6052 rectangular hi/low beam) and those for four headlight systems (4000 round low beam, 4001 round hi beam, 4652 rectangular low beam and 4651 rectangular high beam).

Most of those older-style sealed beams were originally standard incandescent lamps. In 1978, the federal government revised its headlamp regulations to allow the use of "halogen" sealed beams. Halogen lamps are brighter and last longer than regular lamps because the bulbs contain a small amount of bromine gas (one of five elements in the halogen chemical family). The bromine gas allows the use of a smaller, hotter tungsten filament because bromine redeposits the microscopic particles of tungsten that boil off the filament back onto the wire. This extends the life of the bulb and prevents the glass from darkening as the bulb ages.

Halogen lamps are a good upgrade for these older sealed beam applications because halogen lamps produce more light with the same or less current. Halogen sealed beams have an "H" prefix on their part number and are available in various sizes for round, rectangular and low-profile rectangular headlamps.

How much brighter are they? A conventional incandescent bulb generates 16 to 18 lumens of light per watt compared to 20 to 22 or more lumens per watt for a standard halogen bulb (some high output halogen bulbs produce as much as 28 to 33 lumens per watt). The higher output of a halogen headlamp throws more light on the road to improve nighttime visibility and extend the driver's visual range. The light is also whiter than a regular incandescent bulb, which improves visibility too.

In 1983, the federal government approved the use of "composite" headlight assemblies with plastic covers and replaceable bulbs. This gave the vehicle manufacturers more design freedom, reduced the lighting system's vulnerability to stone damage and made it easier in many instances to replace a headlamp. But it also spawned the introduction of a growing number of new halogen bulb configurations.

Some of the more popular replacement halogen bulbs include 9004, 9007, 9008 and H4 for two headlamp systems, 9006, H1, H7 and H11 for low beam quad headlamp applications and 9005 and H9 for the high beam on quad lamp systems. For fog and auxiliary lamps, other popular halogen replacement lamp sizes include 9040, 9045, 9055, 9140, 9145, 9155, H3 and H8.

XENON HEADLIGHTS
In the late 1990s, two new types of "xenon" headlamps were introduced. One type is the High Intensity Discharge (HID) Headlights
that use a special high voltage bulb that contains no filament. Inside the HID bulb are two electrodes separated by a gap and a mixture of xenon gas, mercury and halide salts. A ballast unit steps up the base voltage supplied to the HID lamp to create an electrical arc between the electrodes. This produces a "plasma discharge" inside the bulb that gives off a brilliant bluish-colored light.

HID lighting systems are much more efficient than standard halogen headlamps, producing about 75 lumens per watt. And because a HID bulb has no filament to burn out, they last three to five times longer than a standard halogen bulb. But the required ballast electronics also makes HID lighting systems very expensive so they're currently only used on high-end luxury cars like Mercedes, Porsches and Lincolns. HID replacement bulbs include D1S, D1R, D2s and D2R. Aftermarket HID lighting kits are available to upgrade a vehicle's lighting system but can cost up to $600 or more!

A more affordable upgrade alternative is the second type of xenon headlamps that are now available: the "blue bulbs" that are becoming a popular replacement for standard halogen bulbs. Aftermarket xenon bulbs have a tungsten filament like a standard halogen bulb, but also contain xenon gas that allows the bulb to burn hotter and brighter (up to 30 percent more light depending on the application). A special blue coating on the surface of the bulb helps recreate a bluish light that is similar in appearance to that produced by a more expensive HID lighting system. Best of all, the blue bulbs don't cost much more than standard halogen bulbs.

FINDING THE RIGHT BULBS and LAMPS
With all types of lighting applications, finding the right replacement bulb is essential. Small bulbs, in particular, can be difficult to match. Always refer to a lighting products catalog for the vehicle application. Comparing bulbs and referring to the number on the old bulb is also a good idea - but keep in mind that the old bulb may not be the correct one for the application if it has been replaced before (maybe that's why it burned out). Two bulbs that appear to be the same may have different wattage and resistance ratings. Using the wrong bulb may cause premature bulb failure, circuit overloads or other problems.

On some newer vehicles, "light out" modules are used to sense failed bulbs and alert the driver when a lamp fails. If a replacement bulb does not have the same resistance and wattage rating as the original, it can sometimes cause the module to illuminate the "light out" warning lamp even though the bulb is working.

With halogen and xenon headlamps, the lamp receptacle in the headlamp housing and wiring connectors are configured differently to eliminate the risk of installing the wrong replacement bulb.

CAUTION: DO NOT touch a halogen bulb when you install it because the oil from fingerprints can cause a high temperature bulb to fail prematurely.

It's also a good idea to check the fuses, and buy some extras for future emergencies.

AFTERMARKET HEADLIGHTS & OFFROAD HEADLIGHTS
All kinds of aftermarket headlamps with high candle power ratings are available for vehicles today, but many of these products are labeled for "off-road" use only because of their extremely high output. If you are installing extra headlights on a car, truck or SUV, keep in mind that extra headlights pull extra amps from the charging system and battery. Depending on the wattage of the headlights, you may have to replace the stock alternator with a higher output alternator. The stock alternator may not be able to handle the higher loads and may fail prematurely or allow the battery to run down.