Interpretation ID: nht87-2.48

TYPE: INTERPRETATION-NHTSA

DATE: 07/13/87

FROM: AUTHOR UNAVAILABLE; Erika Z. Jones; NHTSA

TO: Mr. M. Arisaka

TITLE: FMVSS INTERPRETATION

TEXT:

AIR MAIL

Mr. M. Arisaka Manager, Automotive Lighting Engineering Control Sect. Stanley Electric Co., Ltd. 2-9-13, Nakameguro, Meguro-ku Tokyo 153, Japan

Dear Mr. Arisaka:

This is in reply to your letter of November 12, 1986, to former Chief Counsel Jeffrey Miller, concerning the photometric reference this for a two lamp headlamp system, and location of aiming pads.

Your first question is what is the mechanical axis for performing photometry tests where the upper beam in a dual beam headlamp if provided by HB3 and HB4 light sources. As you know, the answer is simple for a single bulb sealed beam headlamp of symmetri cal dimensions: a line perpendicular to the aiming plane through the geometric center of the lens (SAE Standard J579c). Thus, the reference axis for the lower beam of your system would be the geometric center of the portion of the lens that is illuminate d by the HB4. The reference axis for the upper beam is not as easy to identify. Theoretically it should be the center of the light pattern that is produced by the two bulbs. This point would probably be somewhere between the midpoint of the axes of the H B3 and the HB4 and the axis of the HB3. This point is not shown on any of your drawings. However, since the intensity of the lower beam is usually less than 5000 cd at rest point H-V, the theoretical point described above will be very close to the axis o f the HB3. For this reason, the axis of the HB3 should be used as the reference axis for your system. In summary, your Case 1 Table A depicts the proper reference axes.

You have also asked where the aiming pads ought to be located on such a headlamp system, saying that NHTSA's interpretation letter of September 6, 1985, indicated that the pads should be placed on the lower beam portion of the lamp's lens, but that lamps twisted on which they were placed elsewhere. Our 1985 letter was written at a time when experience with these lamps was limited. We now believe that the pads can be located anywhere that will permit proper mechanical aiming, proper reference for photome tric purposes, and that do not interfere with the forming of the beam. Therefore, either of the two locations you present, or any other location, is acceptable provided that the three conditions mentioned above are met.

I hope that this answers your questions.

Sincerely,

Erika Z. Jones Chief Counsel

November 12, 1986

Mr. Jeffrey R. Miller Chief Counsel Department of Transportation National Highway Traffic Safety Administrator 400 Seventh Street, S.W. Washington, D.C. 20590 U.S.A.

Dear Mr. Miller,

Re. Photometric reference axis for two lamps system, and location of aiming pads

We would like to know a view of the photometric reference axis for two-lamp system with two bulbs (HB3 and HB4), and location of aiming pads.

In case that both HB3 and HB4 are used for the upper beam, where the reference axis for 'the upper beam and the lower beam should be placed in photometric measurement? We show examples of reference axis in Table A.

In addition to the question above, we would like to know where the aiming pads of two-lamp system with two bulbs are located. (Please see Table B.)

On your letter of September 6, 1985, the aiming pads should be located on the optical axis of the lower beam portion (HB4) of the headlamp. But now, there is a lamp which aiming pads is located on the other location in the U.S. market. We would like to k now the view of NHTSA again.

We are looking forward to your reply to our questions. Sincerely yours, Stanley Electric Co., Ltd.

Sincerely yours,

Stanley Electric Co., Ltd.

A. Arisaka Manager, Automotive Lighting Engineering Control Sect.

Enc. Table A : Reference axis in photometric measurement Table B : Location of the aiming pads

SEE HARD COPY FOR GRAPHIC INFORMATION