Mr. Vann H. Wilber
Director
Vehicle Safety & International Department
American Automobile Manufacturers Association
1401 H Street, N.W.
Washington, D.C. 20005

Re: Definition of Optical Axis of a Headlamp

Dear Mr. Wilber:

This is in reply to the letter of October 23, 1997, that you and Jeff Erion wrote pointing out a possible inconsistency in the interpretation we provided Steve Law on June 16, 1997, and "the conclusions of the Regulatory Negotiation (Reg Neg) on this subject." Mr. Law had asked whether certain marking configurations met the requirements of paragraph S7.8.5.3(f)(1) of Standard No. 108.

In brief, we advised Mr. Law that markings at the center of each of the four sides of a rectangular headlamp were insufficient to denote the optical axis, which runs directly through the center of the headlamp at 90 degrees to the lens face. However, the final rule and its preamble are silent as to the type of mark that must denote the optical axis. You say that the Reg Neg Committee determined that "marks on the periphery of the lens which could be converged to the center of the lens" would be acceptable, and that Mr. Law's Option C meets this requirement.

The marks on Option C are located at the center of each of the four sides, oriented at 90 degrees from the side. If lines are drawn between opposing sides, they will converge at the center of the headlamp, at the optical axis. We agree that this is a sufficient indication of the optical axis to meet the requirements of paragraph S7.8.5.3(f)(1), and that Mr. Law's Option C is acceptable. This reverses our opinion on Option C that we provided Mr. Law on June 16, 1997.

However, the marks on Option B, located on each side, are parallel to the side. This means that lines drawn between opposing sides will not necessarily intersect on the optical axis unless they are drawn from the center of each line, which is not marked. Option B thus remains unacceptable because lines cannot be converged to the center of the lens from any point on the marks located at the sides of the headlamp.

We are providing Mr. Law and Mr. Erion with a copy of this letter.

Sincerely,
John Womack
Acting Chief Counsel
cc: Steve Law
Jeff Erion
d.12/22/97
ref:108