In Focus: Side/rear lighting: To LED or not to LED?

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Price aside, light-emitting diodes and incandescents are not created equal. LEDs aren’t light bulbs – at least in the traditional sense. A conventional incandescent light bulb consists of a filament, enclosed in glass, in an inert atmosphere. When electric current passes through the wire, resistance causes the filament to glow white-hot. The inert atmosphere keeps the filament from burning up immediately. But eventually, at somewhere between 200 and 15,000 hours, the filament burns out, and the bulb must be replaced.

An LED is a solid-state semiconductor, which emits light when electrical current is passed through it. Clusters of LEDs, hooked up in parallel, can meet the photometric requirements of truck and trailer lighting thanks, in part, to advances in lens design.

There are several advantages to LEDs. First, with no filament to burn out, they live far longer than incandescent bulbs. By some estimates, they can last more than 100,000 hours, which is possibly longer than the life of the vehicle they’re installed on. That’s good for reducing downtime and – in the case of trailer marker lights – keeping mechanics off ladders, thus reducing injury risk in the shop.

LEDs also draw less current, and put less load on a vehicle’s alternator and batteries. Also, since they require less power, they make more power available to trailer antilock braking systems (ABS), thus helping ensure proper operation. This is especially important for doubles and triples, where power is significantly compromised by the large number of lights and the length of wiring.

The Technology & Maintenance Council (TMC) has addressed the issue of current draw in its Recommended Practices (RPs). TMC RP 137, “Antilock Electrical Supply from Tractors Through the SAE J560 Seven-pin Connector,” and TMC RP 141, “Trailer ABS Power Supply Requirements,” constitute a performance standard for tractor and trailer ABS.

RP 141 specifies that a minimum of 9.5 volts should be available to the trailer ABS to ensure proper operation. Because of their high current demand, incandescent lamps contribute greatly to the problem of voltage drop. And by incorporating LED lighting, advises TMC, the amount of voltage drop will be significantly less than that of incandescent lamps.

On average, an LED marker lamp requires 0.05 amps at 14 volts, whereas a typical incandescent light requires 0.4 amps. An average LED stop lamp requires 0.5 amps at 12.8 volts, and a typical incandescent stop lamp requires 2.1 amps.

Given these examples, it’s not hard to see that the cumulative effect of LED lighting all around can significantly reduce current draw and voltage drop.

Finally, LEDs also may offer a safety advantage since they light up approximately 200 milliseconds faster than incandescent bulbs. At 55 mph, a vehicle travels about 16 feet in that time, so the safety margin is something like 1.5 Hondas.

Traditionally, the major drawback to LED lighting has been cost, but that’s changing. Just a few years ago, there was anywhere between a seven to 12-fold premium (over incandescent) for LEDs. Now, costs are about three to four times that of an incandescent counterpart.

Two other considerations:

  • LEDs don’t draw enough current to trip some mechanical turn-signal flashers, so LED-compatible flashers may need to be spec’d.
  • LEDs are diodes and, by definition, current can only flow through them in one direction.

So a concern comes into play when making “custom” repairs. Mechanics who don’t know LEDs are polarized may somehow manage to defeat the directional connectors and hook them up backward. When this happens, they may assume the LEDs are defective, toss ’em, and go back to the parts room for new ones.

To help fleet managers decide if LEDs are right for them, TMC has developed a return-on-investment calculation chart (shown right). Try plugging in your own numbers, and you may find that the ultimate decision isn’t really all that hard to make.

The primary suppliers of rear and side lighting products, both incandescent and LED, are:


LED return on investment (ROI)
Based on its investigation, TMC developed the following formula for equipment users to calculate the return-on-investment time associated with the use of LEDs versus incandescent lamps.

To calculate potential savings by the use of LEDs, enter your fleet’s data. In order to perform the necessary calculations, use the following formula:
1. Number of lamps: ___________
2. Price of incandescent: $__________
3. Price of LED: $__________
4. Investment per lamp: $__________ (line 3-2)
5. Investment: $__________ (line 1Ă—4)
6. Life of incandescent: ___________ (years)
7. Changes/year: ___________ (lines 1/6)
8. Maintenance time: ___________ (Hours per change)
9. Labor rate: $__________ (rate/hour)
10. Savings: $__________ (lines 9x8x7)
11.Vehicle downtime rate: $__________ (rate/hour)
12. Downtime saved: $__________ (lines11x8x7)
13. Investment: $__________ (line 5)
14. Yearly savings: $__________ (line 10+12)
15. In years: ___________ (line 13/14)