Interpretation ID: 1985-01.5

TYPE: INTERPRETATION-NHTSA

DATE: 01/04/85

FROM: AUTHOR UNAVAILABLE; Frank Berndt; NHTSA

TO: Brian Gill -- Senior Manager, Certification Dept., American Honda Motor Co., Inc.

TITLE: FMVSS INTERPRETATION

TEXT:

Mr. Brian Gill Senior Manager Certification Department American Honda Motor Co., Inc. P.O. Box 50 Gardena, California 90247

This is in response to your letter of May 25, 1984, asking for an interpretation of Motor Vehicle Safety Standard No. 108. Table IV specifies that the minimum horizontal separation distance "(centerline to centerline of lamp)" for rear turn signal lamps on motorcycles is 9 inches. You have asked whether the "centerline" refers to the distance between the lens centers, between the centers of the effective projected luminous areas, or between the bulb centers.

You asked for confirmation of your belief that the proper interpretation is found in the referenced SAE Standard, J588e, which contains the language "Optical axes (filament centers)," implying that the correct distance is that between the "bulb centers" as you term it.

We find no direct correlation between the phrases "centerline to centerline of lamps" and "optical axis (filament center) ." The lamp is a device emitting light whereas "optical axis (filament center)" does not refer to the lamp but only to a portion of its light-producing component. As that phrase is used in SAE J588e, it defines the method of measuring distances between bulbs in multi-compartment lamps for the purpose of testing for photometric requirements (paragraph 3.1), or in measuring the separation of the turn signal from the headlamp (paragraph 4.2, where, incidentally, it is expressed as the distance between filament and a lamp component, the retaining ring).

Taken literally, "centerline to centerline of lamps" in our view means the distance between lens centers. In the response to petitions for reconsideration of the center high-mounted stoplamp amendment (May 17, 1984), the question was asked whether the "center" of the lamp was its geometric center, its optical center, or the center of the bulb filament. The agency replied that the center of the lamp is the geometric center. Since the purpose of the minimum separation requirement is to insure that the turn signal is perceived as such, we believe that the correct interpretation of "centerline to centerline" is a measurement from the geometric center of one lamp to the geometric center of the other lamp. The geometric center would be anonymous with the term "geometric centroid of lens" as used in SAE J1221 Headlamp-Turn Signal Spacing. Sincerely,

Frank Berndt Chief Counsel