Hector Fratty

By Daniel Stern, Driving Vision News 

Everyone knows the benefits of LEDs for brake and signal lighting: they last forever, they light up quickly, they take much less power than a filament bulb to produce equivalent light, they offer new packaging and styling possibilities, and so on. But there are pesky new difficulties arising, as often happens when new technologies collide with older testing and regulatory practices.

LED brake and tail lamps have quickly and almost completely come to predominance on trucks and buses in North America. In that market, almost all large commercial vehicles use one of just a few standard rear lamp formats, by far the most popular of which is the 100mm (4-inch) diameter round. Lamps of this format are the smallest circular lamps that meet the U.S. Effective Projected Luminous Lamp Area (EPLLA) requirement. On vehicles wider than 203 cm, brake and tail lamps must have an EPLLA of 75cm² . It is not permitted to accumulate the required EPLLA with multiple lamps; no matter how many brake and tail lamps are fitted, each and every individual lamp must meet the EPLLA requirement by itself. An ordinary bulb-type 100mm lamp (accounting for occlusion by the mounting bezel) is just barely above 75cm²; its whole lens area is lit. But most LED 100mm round lamps use multiple emitters. When powered, these lamps produce a visual signal of between 5 and 40 dots with dark space amongst the emitters.

The dark space isn’t lit and so can’t be counted when calculating the lamp’s EPLLA. But the regulation does not provide a definitive method for measuring a lamp’s EPLLA. The assumption, based on lamps equipped with conventional filament bulbs, is that the only unlit areas might be round the edges of the lamp. Compliance testing labs and industry working groups have devised and proposed various methods of measuring EPLLA, and some of these appear to give consistent, realistic, repeatable results—but none of them is an official method. Meanwhile, American regulators have raised concerns about lamps on the road that don’t meet EPLLA requirements, but there’s been little enforcement action, probably due in part to the lack of an official test protocol. For now, there are noncompliant lamps on the road and nobody’s quite sure what to do about it.

Nor is it entirely clear what the relative safety effect is of this particular kind of noncompliance.