Interpretation ID: aiam4353
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 Chie Counsel Jeffrey Miller, concerning the photometric reference axis for a two lamp headlamp system, and location of aiming pads.; Your first question is what is the mechanical axis of performin photometry tests where the upper beam in a dual beam headlamp is provided by HB3 and HB4 light sources. As you know, the answer is simple for a single bulb sealed beam headlamp of symmetrical 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 illuminated 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 HB3 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 test point H-V, the theoretical point described above will be very close to the axis of 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 references axes.; You have also asked where the aiming pass ought to be located on such headlamp system, saying that NHTSA's interpretations 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 existed 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 photometric 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