Interpretation ID: nht90-1.88

TYPE: INTERPRETATION-NHTSA

DATE: MARCH 29, 1990

FROM: STEPHEN P. WOOD -- ACTING CHIEF COUNSEL, NHTSA

TO: J. BRETTSCHNEIDER -- ROBERT BOSCH GMBH

TITLE: NONE

ATTACHMT: LETTER DATED 8-31-89 TO RICHARD VAN IDERSTINE, NHTSA, FROM J. BRETTSCHNEIDER, ROBERT BOSCH GMBH, ATTACHED.

TEXT:

This is in reply to your letter to Mr. Van Iderstine of this agency, with reference to the performance of the impact test according to SAE J1383. I regret the delay in responding.

You state that according to paragraph 4.10.3 of J1383, the impact test is conducted along the mechanical axis, and that paragraph 2.14 of SAE J579 defines the mechanical axis as perpendicular to the aiming plane through the geometric center of the lens. With respect to this, you have asked two questions: "where is the geometric center of a lens without aiming pads?", and "where is the geometric center of a lens which moreover covers two compartments, one for the lower beam and one for the upper beam?"

First, we must advise you that the impact test of J1383 is not required for any headlamp covered by Federal Motor Vehicle Safety Standard No. 108. The impact test that is required for integral beam and replaceable bulb headlamps is specified in section S8.8, and we shall answer your questions with respect to its provisions.

S8.8 states in part that "one impact shall be delivered to the center of the lens on the mechanical axis." This language originated in 1983 with the adoption of specifications for replaceable bulb headlamps, when a headlamp was not permitted to incorporate more than one light source. Thus, the lens center and mechanical axis were coincident. Now that Standard No. 108 permits two standardized replaceable light sources in a headlamp, there are two mechanical axes. We also note that lamps may now use Vehicle Headlamp Aiming Devices, and thus have lenses without aiming pads. As we understand your concern, you appear to be uncertain as to the location of the impact for the test of section S8.8.

After reviewing your letter, we have concluded that the language "on the mechanical axis" is a redundancy. Thus, the impact should be applied on the center of the lens, without reference to the mechanical axis. We consider the center of the lens to be the intersection of the lens and a line which is parallel to the longitudinal axis of the vehicle and passes through the centroid of the projected lens area as viewed on a plane perpendicular to the longitudinal axis of the vehicle.

We shall be pleased to answer any further questions you may have.