Bottom Line

by Paul Abelson, technical editor

Lights can be considered as a maintenance headache or as useful tools, depending on your point of view. Since most of our sensory input while driving is through our eyes, we'll first examine lighting as a useful tool.

You can categorize lighting into two types: forward lighting, used to allow us to see what we need to, and all other lighting: clearance, marker and stop-turn-tail lights, designed to help others see us, identify us and understand what we'll be doing in the immediate future. Each of these broad categories can be further broken down by function.

Many of us remember the time when truck headlights only came in seven-inch round incandescent. Their light output was adequate when fleets operated 238s and 263s, and when most owner-operators ran 290s and 318s. (For those of you unfamiliar with those numbers, they were the horsepower ratings of popular engines a generation or more ago.) Today, more power and new, higher speed laws mean a greater need for better forward lighting.


Traditional headlights that many trucks use, seven-inch round and eight-inch rectangular low beam/high beam units, have a low beam range of about a quarter of a mile. High beams reach to about 4,000 feet. Light output varies with voltage and so does lamp life.

As voltage increases, so does light output, but life decreases. Voltage is lost due to resistance in long wiring and switches. Jacobs Electronics, a well-known electrical controls supplier for performance cars, makes the Headlight Brightener, a system of wires and relays that brings current to the headlights directly from the alternator. This assures full voltage at the headlights, resulting in a 40 to 60 percent increase in brightness, with a whiter, clearer light. Since the voltage regulator limits alternator voltage, voltage to the headlights is limited and should not shorten lamp life significantly.

Today, almost all truck headlights are halogen, a light source about 35 percent brighter than incandescent. Light is more controlled, too, with the development of better reflectors and improved lenses. Most lighting improvements tend to come from automobiles, then find their way onto trucks. One new form of lighting has already made its mark on luxury cars. High intensity discharge (HID) lights, pioneered by Osram Sylvania, create a miniature arc lamp inside a bulb. HIDs operate on only 35 watts, compared to 55 watts needed for halogens. HID light output, 3000 lumens, is triple that of the best halogen bulb. Light output is broader and more even, as the accompanying photographs show.

driving lights

For those of us who don't want to wait for our truck makers to incorporate these advances into their next designs, auxiliary lighting can provide the answer. Most of us are familiar with long-range driving lights, those un-patterned beams of high intensity light that let us see a half-mile or more ahead…but only ahead. And these "flame throwers" have to be turned off whenever high beams should be off; within 500 feet of another vehicle, either oncoming or being overtaken.

Today, more power and new, higher speed laws mean a greater need for better forward lighting

Hella, the German lamp and electrical parts company with facilities in five American states, has a better idea. Their XL "Extra Light" fits in the same housing as the 550 FF fog light, but has a light pattern design to supplement headlights. The XL increases light to the side, but its best feature is that it can be left on at all times, since its output and pattern is similar to halogen low beams. Hella recently introduced Vision Plus replacement halogen headlights, in traditional seven-inch round and five-inch rectangular shapes. They have broader light patterns, and their high beams reach out about a mile. They use HB2 bulbs that generate 55 watts on low beam and 60 on high. Vision Plus is DOT approved in all 50 states. They are costly, almost ten times the on-sale price of ordinary headlights, but if improved vision is important to you, the one-time investment may be worthwhile. Replacement bulbs are under $10.00 each. You can use the XLs with Vision Plus for the ultimate in lighting, at least until HIDs become available.

fog lights

Fog lights are special purpose lights designed for misty rain, fog and snow. These conditions can reflect light back into a driver's eyes, so they feature mechanisms that prevent that. Hella and others use optics to keep a flat top on the light. Per-Lux, now owned by Grote, became a popular fog light among truckers because the lamps came with angled louvers. They prevent stray light from angling upward and minimize glare. No matter what the design, fog lights must be aimed properly (see sidebar) to be effective.

Aiming your fog lights

Here's an easy way to check the aim of your fog lights. Pull your truck perpendicular to a flat wall, making sure it's on level ground. You should be about 20 to 30 feet from the wall. Hold a level at the height of the center of the fog lamps and sight along it to the wall. Have a friend mark the point with a crayon. Now measure how far your truck is from the wall, and multiply that distance by 0.03. If, for example, you're 24 feet 7 inches from the wall, or 295 inches, multiplying that by 0.03 yields 8.85 inches. In round numbers, the top of the bright spot of the beam pattern should be eight and seven-eighths inches below the mark on the wall. In any case, there should be little, if any light from the lamps above the mark on the wall.

Some newer lamps have such an even distribution of light, it's hard to determine where the bright spot is. In that case, just make sure the cutoff is at or below the mark on the wall.


Clearance and marker lights are designed to let other vehicles see you. In the early days of trucking, when horsepower ratings identified engine makers, all identification lighting had replaceable bulbs. They were (and still are) susceptible to shock, vibration and surge currents. They didn't last long, but were easy to replace using just a screwdriver. Shortly after World War II, a new company pioneered the use of sealed, shock and vibration resistant lighting specifically designed for heavy trucks. Since then, Truck-Lite has been an innovator in heavy-duty lighting. Sealed lights, warranted for three years and usually lasting far longer, have become the standard for most fleets. They realize that the higher cost of sealed lamps is more than offset by the huge reduction in replacement labor, not to mention bulb cost. Truck-Lite's "Vehicle Lighting Life Cycle Cost Estimator" is a computer program that calculates costs based on your actual experience. For a typical trailer kept seven years, maintaining bulb-replaceable lights can cost almost $2,000 per year in parts and labor, while sealed lighting can save more than 90 percent of that cost. This estimate doesn't include tickets for lights being out.


Light emitting diodes, or LEDs, offer even greater savings due to their extra long life. LEDs last longer than most trucks do. They draw a small fraction of what the current incandescent bulbs do, they resist shock and vibration and burn cooler. Rumors persist that snow and ice build up around LEDs, but Brad Van Riper, Truck-Lite's vice president of engineering, reports no customer complaints in all the years LEDs have been available. Customer acceptance has grown dramatically. Van Riper reports that about 10 percent of new trailers are LED equipped, and he expects that to exceed 25 percent in just a few years.

LEDs have another advantage when used for brake lights. They light instantly, while bulbs or sealed lamps take about 0.2 seconds to heat up to glowing temperature. At 60 mph, that translates to 17.5 feet of additional warning time for following vehicles.


LEDs have one disadvantage. They are very directional, with a narrow, nearly horizontal light pattern. If you're used to using your markers to light your way backing in between two rigs at the truckstop, you'll be backing blind with LEDs. They'll light a narrow strip of the rig along side, but you won't see the ground. If you switch to LEDs, you might want to keep a sealed incandescent light at each rear corner of your trailer. Better yet, install backup lights.

For backing and cornering, Trailer Safety Light Manufacturing has an under-trailer lighting system that floodlights the area in front of the tandems. It's triggered by the turn signals or four-ways, to provide ample light for maneuvering.

light maintenance

To avoid maintenance problems, start with quality products from reputable manufacturers. Heat, vibration, excessive voltage and corrosion are among lighting's worst enemies. To avoid heat build-up, leave a gap between trailer lights and docks, so air can circulate to cool the lamps. Dirt and dried salt not only block light output, they insulate and keep heat in. Clean lights often. When using bulbs or sealed lighting, use rubber mountings to minimize shock loads. LEDs don't need this protection, so they can be flange-mounted for theft prevention. To protect against voltage surges that shorten filament life, make sure your lights are off before starting your engine, your generator, a microwave or any device with a high current draw. Finally, follow good wire maintenance practices, including the generous use of a di-electric compound, like Truck-Lite's NYK, whenever you make any connections. LL