Interpretation ID: nht92-6.38

DATE: May 25, 1992

FROM: Guy Dorleans -- International Regulatory Affairs Manager, Valeo

TO: Chief Counsel, NHTSA

TITLE: None

ATTACHMT: Attached to letter dated 7/7/92 from Paul J. Rice to Guy Dorleans (A39; Std. 108)

TEXT:

Standard 108 specifies different levels of photometric requirements for signal lamps, depending on the number of lighted sections which they have. The highest values are mandatory for those functions obtained by "three lighted sections", as per relevant subparagraph 5.1.1.11 Fig 1b, title 49 in the Code of Federal Regulations.

The use of light-emitting diodes does not permit to distinguish at a glance several distinct lighted sections, because the small size of each individual light source produces an even illumination on the lens. These light sources can not be subjected to voltages bigger than 1,5 Volts, and current state-of-the-art compels the equipment manufacturer to group them in arrays, each of these arrays containing a few diodes in series.

In the case of failure of one diode or its solder, a variation of the illuminance on the lens will be easy to identify. The inner wiring of the diodes will either produce a completely dark array, or increase the brilliance of those diodes not affected by the defect.

In the event where light-emitting diodes, or other non-removable light sources are used in quantities bigger than three, we consider that the provision for "lamps with three lighted sections" applies A FORTIORI, because its severeness will keep the user on the safe side even if the Standard does not specifically address the problems raised by the multiple light sources.

We hereby ask confirmation that our interpretation is correct.