Interpretation ID: nht89-1.53

TYPE: INTERPRETATION-NHTSA

DATE: 03/27/89

FROM: SHUICHI WATANABE -- MANAGER, AUTOMOTIVE LIGHTING HOMOLOGATION SECT. STANLEY ELECTRIC CO, JAPAN

TO: ERIKA Z. JONES -- CHIEF COUNSEL DEPARTMENT OF TRANSPORTATION NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION

TITLE: MEASUREMENT OF INCIDENT LIGHT ANGLE

ATTACHMT: ATTACHED TO LETTER FROM STEPHEN P. WOOD OF NHTSA TO SHUICHI WATANABE OF STANLEY ELECTRIC CO OF JAPAN; REDBOOK A34, STANDARD 108

TEXT: Dear Ms. Jones,

According to SAE J587 Oct 81 6.5 and Fig. 3 which is quoted by present FMVSS No. 108, it says,

This angle being measured from the edge of the light emitting surface of the device farthest from the surface of the plate.

In order to determine the farthest point on the light emitting surface, we understand that only the distance "1" between license plate and a plane runs parallel to it should be considered and not by distance "m" nor "n". (See Fig. A of attached paper.) This also means that in the case of round and dome shaped license plate light (Fig. B), you will easily find only one point "p" as the farthest point. But if the farthest point can exist so may on a line or a plane as described in Fig. C or D, how could it be determined? Should it be for instance, left end, right end or center of them? We also have same question for E and F.

It will be very much appreciated if you could give us a clear discrimination.

Yours faithfully,

ATTCH: [ATTACHED DIAGRAM OMITTED]