There has never been any doubt about the advantages of LED lights. They last longer, reduce maintenance, draw less power, increase the margin of safety, and are more resistant to shock.

Yet these benefits have come at a cost that, until recently, was too high for most fleet managers. But with new technology driving down cost and recent mandates for antilock brakes on trailers, fleets are looking at LED technology again. And they like what they see.

"Antilock braking is changing the landscape," says Dominic Grote, marketing manager for Grote Industries. "The power requirement for ABS puts additional demands on the electrical system. You run the risk of drawing down the power needed for ABS, especially in multiple trailer applications with incandescent lights. "

The industry has agreed that at least 9.5 volts are needed to power the brakes. That makes LEDs an attractive option because they offer one-eighth the amp draw of their incandescent cousins.

It doesn't hurt that the cost differential between LEDs and traditional incandescents is narrowing. "Price has been an obstacle," admits Matt Forner, LED product manager for Grote. When they were first introduced in 1992, the lamps cost ten times as much as incandescents. Today, it's more like five to one -- the result of improved technology and added buying clout. "We're buying significantly more diodes for lamp production than in the past," says Forner. "That increases our leverage." It also opens doors in vocational fleets such as refuse and construction that are looking for more robust lights to eliminate the amount of breakage.

Not only are more diodes being produced, they are getting better. New diodes put out four times the light of first-generation models. Couple that with improvements in optics and lenses, and manufacturers can now take diodes out of current designs and still comply with federal regulations.

Today's red marker light, for example, needs just two LEDs to produce the light for which six were required in early models. Amber lights have seen similar reductions, going from nine diodes at the beginning to three today. "In the near future, we'll get to the point where we need only one diode for red marker lamps," predicts Grote.

U.S. manufacturers use the Hewlett-Packard diodes. But as these diodes become more popular, new companies are eyeing the market. And there's the rub. Many of these new entrants build an inferior non-sealed unit. "Sealed lights keep the water from getting inside and causing destruction," says Darryl Bent, senior project engineer for Peterson Manufacturing.

"The overseas lights are not sealed. They put a really inexpensive LED circuit board inside a name brand housing and lens, and market it with very low-ball pricing," Bent adds.

While these lamps don't meet federal standards, their lower prices may result in some market penetration. "There will be a large sector that may be swamped by a cheap product," adds Peterson's Larry Vickers, heavy-duty sales manager. "I don't want that sector to give LEDs a black eye."

Technology improvements are not limited to the diodes themselves. Because the lamps draw less power, wiring requirements can range from the 14-gauge wire typical on lighting harnesses to the 18-gauge wire used in the cab. There is also the possibility that 16-18 gauge wire can be used for the jumpers on the trailer.

While this may be true, many fleets stick with the beefier wiring that will support incandescents in the event of an on-road failure, when LEDs may be tough to track down. Because LEDs are not a common stock item, finding them in the field remains spotty, at best.

A major concern for LED manufacturers is to produce a quality lamp that is put on a unit with inferior wiring or harnesses. "You have to ensure the infrastructure is in place to support LEDs," says Bent. "You have to take a systems approach." That explains the popularity of modular harnesses that help seal out moisture and prevent electrical shorts.

Improvements in the diode technology and price have spurred manufacturers to introduce a broader line of product offerings, including interchangeable mountings and design. This ensures that more LEDs will fit more applications.

"The increasing breadth and depth of the product line has begun to create some economies of scale," says Bob Ives, director of sales and marketing for Truck-Lite. "Over the past two or three years, the price of diodes has been cut in half. But it's not a linear progression. Those cost reductions may not continue at that magnitude."

Although LEDs still carry a hefty upcharge -- up to five times that of incandescent lamps -- the longevity and performance of the bulbs help return the value to the fleet. In fact, a new CD-based program now available from Truck-Lite allows fleets to plug in specifics from their own operations, including types of lamps, number of lamps, typical replacement intervals, and labor rates, and come up with a cost savings.

An incandescent version of a marker lamp, which typically would be used in such life-cycle cost analysis, would be replaced two to three times in five years. At a cost of $2-$3 for the bulb and an average shop rate of close to $60/hour, fleets should plan on $18 to replace the average light. Stretch that figure across the entire trailer for its 10-year duty life and the costs could easily approach $500 per trailer, says Dominic Grote. Compare that to the $15 upcharge for an LED light that probably won't need to be replaced over the same trailer life, and the savings are dramatic.

In addition, if that marker light is on the top rail it presents more exposure to injury as technicians have to drag out a ladder, climb to the top, and make the replacement. That concern has led many fleets to spec a hybrid system: LEDs on the top rail and incandescents on the bottom.

One less tangible benefit is the margin of safety. Since LEDs focus the light better, the units typically are more visible from farther away. Plus, they power up more quickly than incandescents. The driver of a vehicle traveling at 65 mph behind one equipped with LED stoplamps will have 24 more feet of stopping distance than a driver traveling behind one with incandescent lights, according to a study conducted by the University of Michigan Transportation Research Institute.

The growing popularity of LED designs is also helping to mitigate one of the traditional obstacles to spec'ing the systems in the first place -- theft. "We don't hear as much about theft as we used to," says Truck-Lite's Ives. "The more abundant the supply, the less premium there is."

In addition, manufacturers have developed more theft-resistant flange designs with non-back-out screws or rivets that prevent easy theft.

But the growing popularity of LEDs has also resulted in some unintended consequences. "The weak link in incandescent lighting used to be a bulb going out through shock and corrosion," explains Ives. "You never had to worry about the envelope. The bulb always failed before the weld or before chemicals attacked the housing."

With LEDs lasting upwards of 100,000 hours, the housing and plugs have become the weak links. "Today, we have to worry about ensuring a truly sealed system," Ives adds. As a result, Truck-Lite has added a tough acrylic coating, called DiamondShell, to guard against deterioration of the plastic lens and improve the sealing of the plug area.

The fear is that as the number of diodes needed declines, the industry will bump into a technological ceiling. "As the number of LEDs continues to drop," says Peterson Manufacturing's Bent, "the cost advantage will go to those who can do a better job of assembling it."

TMC RP 137(T) "Antilock Electrical Supply from Tractors Through the SAE J560 Seven-Pin Connector," in conjunction with TMC RP 141(T) "Trailer ABS Power Supply Requirements," constitutes a performance standard for tractor and trailer ABS. The report states, "A minimum of 9.5 volts should be observed when measured from the positive circuit leading to the solenoid (Pin 4) and the ground circuit (Pin 1)."

LED lights require significantly lower current than comparable incandescent lights. On average, an LED marker lamp requires 0.05 amps at 14 volts while the typical incandescent light requires 0.40 amps. Table 1 shows a comparison for current draw of a typical tractor lighting installation and Table 2 compares the current draw of a typical dry van trailer configuration.

(Note: To view tables mentioned in sidebar, refer to article on pages 60-64 of FLEET OWNER's April 1998 issue.)

Incandescent lamps contain a tungsten filament wire. When current flows through the filament it encounters resistance causing the wire to heat up and glow brightly. Over time, the tungsten evaporates and the wire burns out. This occurs somewhere between 200 and 15,000 hours, depending upon the incandescent bulb and the presence of shock and vibration.

By contrast, the LED (light emitting diode) is a solid-state electronic component. When current flows through the semiconductor compounds, light is emitted. With no evaporation of components, and because the diode is in a solid state and therefore not affected by shock and vibration, the life span of an individual LED is longer -- up to 100,000 hours.

(Note: To view diagrams mentioned in sidebar, refer to article on pages 60-64 of FLEET OWNER's April 1998 issue.)