Interpretation ID: nht80-3.20
DATE: 07/15/80
FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA
TO: General Motors Corporation
TITLE: FMVSS INTERPRETATION
TEXT: This is in reply to your letter of April 29, 1980, requesting an interpretation of Federal Motor Vehicle Safety Standard No. 108 with respect to headlamp design. Specifically, General Motors asks whether a headlamp with a mounting tang that differs from the design illustrated in SAE Standard J571d, Dimensional Specifications for Sealed Beam Headlamp Units, June 1976 and SAE Recommended Practice J1132, 142 mm x 200 mm Sealed Beam Headlamp Unit, January 1976 is permissible. It is your opinion that this variance has no effect upon headlamp interchangeability or otherwise affects safety.
As you know, paragraph S4.1.1 requires headlamps to be "designed to conform" to SAE materials incorporated by reference, which include J571d and J1132. The SAE materials contain detailed drawings and dimensional requirements which manufacturers have followed in headlamp design. Standard No. 108 has been criticized for its specificity regarding headlamps although this aspect of it has been judicially upheld as necessary to the overall safety performance of the headlighting system. Standardization through such specificity is necessary to achieve the safety goals of interchangeability and ease of replacement.
To encourage innovation and relieve manufacturers of unnecessary restrictions, as well as to enhance the performance aspects of Standard No. 108, we believe that a manufacturer can certify that its headlamps have been designed to conform to Standard No. 108 without the necessity of strict adherence to the SAE dimensions if the safety purposes of Standard No. 108 are in no way compromised. Principally, headlamps must continue to be interchangeable with those of like nominal dimensions. With this in mind, the tang design postulated by General Motors is not prohibited by Standard No. 108 provided that headlamps incorporating it are interchangeable with those that meet all the design specifications of SAE J571d and SAE J1132.
SINCERELY,