Interpretation ID: 77-1.39

TYPE: INTERPRETATION-NHTSA

DATE: 03/04/77

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Trailer Manufacturers Association

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letter of December 20, 1976 asking for a clarification of the statement in my letter to you dated December 3, 1976, that "the light emitted by one bulb must not be perceived as performing the function of the other in addition to its design function."

It is evident from your letter and others that our previous interpretations of the term "optical combination" have been found to be ambiguous and lacking in the objective criteria that a Federal motor vehicle safety standard must provide. We have reviewed the matter, and now wish to modify our previous interpretation. In our view a lamp is "optically combined" when the same light source (i.e. bulb) and the same lens area fulfill two or more functions (e.g. taillamp and stop lamp, clearance lamp and turn signal lamp). A dual filament bulb would be regarded as the "same light source". In determining conformance, the photometric requirements for clearance and taillamp functions, where two bulbs are located in a single compartment, must be met with only the bulb energized that is designed to perform the specific function. But the 15 candlepower maximum under Standard No. 108, however, would be determined with both the taillamp and clearance lamp bulb energized. Further, the lamp must be located to meet requirements for both clearance and taillamps. Our re-interpretation means that the issue of light spill-over form one area of the lamp to another is irrelevant to conformance.

SINCERELY,

Trailer manufacturers association

December 20, 1976

Mr. Frank A. Berndt U.S. DEPARTMENT OF TRANSPORTATION

Further to my letter of October 29th, and yours of December 3, 1976 (N 40 - 30), the 47 Series Tite Lite contains a No. 57 2 CP bulb serving the clearance and sidemarker lamp functions and a No. 1157 3/32cp bulb serving the remaining functions.

Our question concerning this light was limited to whether the clearance lamp function is considered "optically combined."

Your December 3rd letter indicates that "the light emitted by one bulb must not be perceived as performing the function of the other in addition to its design function." We don't understand the meaning of this statement. In the 47 Series Tite-Lite, the No. 57 bulb provides the clearance lamp design function, yet the No. 1157 bulb which is always lit simultaneously certainly augments the light emitted by the clearance lamp, and will light the clearance lamp lens an appreciable amount if the design bulb was burned out. That would seem a safety feature.

An early response will be appreciated.

Director of Engineering

Donald I. Reed