Last week, Trucks, Parts, Service shined our attention on LED lamps and why — despite their superior design and durability compared to their incandescent predecessors — they still sometimes prematurely fail in commercial vehicle applications.
In our piece we also asked and attempted to answer the question of “How many failed diodes puts a lamp out-of-service?” I say attempted to answer because in the United States, no single answer exists. Federal Motor Vehicle Safety Standard (FMVSS) 108 does not offer a single number or percentage of diodes that can fail within a lamp before it is conclusively out-of-service.
Obviously a completely dead light is a violation and a brand new, fully illuminated lamp is optimal, but between those levels of brightness is a grey area — and not just where individual diodes are no longer operational. It is an inspector’s responsibility to inspect vehicle lighting and determine when lamps are out-of-service, and every inspector’s threshold for what actually puts a lamp out-of-service varies.
[RELATED: Here’s why LED lamps still fail]
That’s not the case in Canada. As reported by TPS sister publication Overdrive Tuesday in a follow-up to last week’s article it was revealed that if “25% or more of the diodes are inoperative” in a lamp in Canada, it will fail inspection in that nation.
Quoting Commercial Vehicle Safety Alliance (CVSA) Roadside Inspection Specialist John Sova, Overdrive says Canada’s rule simplifies things for inspectors but adds determining the performance of a commercial vehicle lamp is actually more complex than a simple percentage equation would indicate.
Size of a lamp, brightness of other diodes, position of a failed diode and other factors all impact how visible a lamp truly is on a roadway, and not every lamp with 25% of diode failures will look the same.
“It gets quite complex when you start digging into it,” Sova says.
Yet Sova also notes ATA’s Technology & Maintenance Council (TMC) has debated creating a baseline standard in the U.S. and the discussion is still ongoing. In the meantime, he reiterates the message from our sources last week, when diodes start to fail, replace the lamp. A dimming or failed lamp is an invitation to a roadside inspection, he says.
“If you’re a trooper and you’re sitting in the median watching traffic go by at 65 miles an hour, what are you going to be able to see at that speed?,” he asks. “It’s the obvious stuff, right? So lighting that’s out is always a real good flashing red light. It pulls your attention.”
