Mr. Robert G. Mills
Supervisor, Homologation and Publications
Triumph Designs Limited
Dodwells Bridge Industrial Estate
Hinckley, Leics. LE10 3BS
Dear Mr. Mills:
This is in reply to your letter of June 17, 2002, seeking a further clarification of the applicability of S18.104.22.168 of Federal Motor Vehicle Safety Standard No. 108 to motorcycle headlamp designs that Triumph is contemplating. You have enclosed two illustrations of potential designs. You referred at various points in your letter to "main beam" and "dipped beam." These are not terms used in Standard No. 108. For purposes of this reply, we assume that "main beam" means "upper beam," and that "dipped beam" means "lower beam."
In our letter of May 24, 2002, to you, we pointed out that the Triumph headlamp design discussed in that letter should be designed to comply with S22.214.171.124(a), rather than S126.96.36.199(b) as you had originally thought. Your review of that paragraph has raised doubts as to whether your design meets that paragraph. The sentence of S188.8.131.52(a) that concerns you reads:
If the headlamp contains more than one light source, each light source shall be mounted on the vertical centerline with the upper beam no higher than the lower beam, or horizontally disposed about the vertical centerline and mounted at the same height.
Illustration 1 depicts two upper ("main") beam and two lower ("dipped") beam light sources, horizontally disposed about the vertical centerline, with the lower beam sources mounted below and inboard of the upper beam light sources. You informed us that your design does not permit mounting all four light sources at the same height, but nevertheless ask whether the design is acceptable since the individual beams will be mounted at the same height. Illustration 2 depicts a "headlamp unit containing three light sources," the center light source providing the upper beam and that the two adjacent light sources, mounted slightly higher, providing the lower beam. You ask whether this three-light source design is acceptable.
The headlamp designs shown in Illustration 1 and Illustration 2 do not meet the design requirements of S184.108.40.206(a) because all light sources are not mounted at the same height, though horizontally disposed about the vertical centerline.
You also asked whether incorporating different numbers of light sources for upper and lower beams, as in Illustration 2, would comply with Standard No. 108. There is no restriction for the number of light sources used in the upper or lower beams of a motorcycle headlamp system designed to conform to the photometry requirements of S7.9.2(a) and the installation requirements of S220.127.116.11.