LED question debated again

How many dead diodes does it take for an inspector to declare an LED tail lamp “failed” and issue you a citation? Probably all of them – depending on the situation and how that inspector interprets current federal or state regulations – according to an official with the Commercial Vehicle Safety Alliance, which sets guidelines for North American enforcement officers.

“Right now, if one diode is still burning, it’s probably OK,” John Sova, a CVSA safety program manager, remarked during an informal conversation after an industry discussion on the subject. But he shrugged as he said it and reiterated that it’s up to an individual officer’s judgment. CVSA instead wants some kind of objective number and is waiting for guidance from ATA’s Technology & Maintenance Council.

Federal regs say that if an officer can see a tail lamp’s light from 50 feet, the lamp is legal. That might have been sufficient in the days of incandescent light bulbs. But TMC and CVSA officials believe that may not be the case now, when light-emitting diodes – LEDs – comprise the illuminating component of most truck and trailer lamps.

The TMC study group, composed of representatives of truck fleets and electrical lighting manufacturers, has been grappling with the question for more than a year. The group wants to define not only what constitutes a legal lamp failure but also when the lamp should be replaced by maintenance people. Ideally, replacement should happen before the lamp becomes illegal.

Last year, one of the manufacturers did some bench testing and concluded that a red LED tail lamp has become dim enough for failure when about half its diodes were out. That was for maintenance purposes, not necessarily for enforcement.

The most recent TMC session was during the organization’s annual meeting, which took place March 3-7 in New Orleans. At a previous meeting in September in Cleveland, members thought they had agreement but now have backtracked. The group is chaired by Jay Davenport, director of OEM sales for Peterson Manufacturing.

Last year, the members wrote and distributed a preliminary recommended practice on the matter. Based on those bench tests that measured illumination, the recommended practice was to replace a lamp if 50% or more of its diodes were out. TMC members as a whole approved the recommended practice, but at the group’s March meeting, some felt the 50% was unreasonable.

Several members noted that diodes are wired in series, with three or four diodes on one circuit. So when one fails, all the diodes on that string go out, like a string of old Christmas tree lights. If a lamp has five or seven diodes, the 50% criterion can be reached quickly. That makes it too stringent and could lead to undeserved citations. The comment by Sova – that one working diode is probably enough to be legal – seems to support that thinking.

Members know that CVSA is waiting for industry guidance and that they are “it,” but they want to be sure they get things right.

That should include more input from lighting manufacturers and other sources, which might comprise the further testing that members called for. Therefore, the current, somewhat nebulous federal reg remains in place, as does the latitude given individual inspectors.

Of course, they can issue citations based on other factors: no tail lights or no stop lights. But these are rare occurrences if rear lamps are getting power, because at least some of the four or six lamps on the rear of most semitrailers still work. One inoperative turn signal also could result in a citation, however. And members of the TMC group noted that individual states have lighting regulations that might be more stringent.

The TMC group could revise that recommended practice, perhaps with one percentage for maintenance purposes and another that suggests legal failure, or leave the failure number to CVSA. Meanwhile, a good idea for safety is to replace the lamp when a few diodes become dim or burn out. LL