Interpretation ID: aiam3876
Vice President
Design and Engineering
Jac Products
Inc.
1901 E. Ellsworth
Ann Arbor
MI 48104;
Dear Mr. Cucheran: This is in reply to your letter of November 30, 1984, to Mr. Vinson o this office asking for an interpretation of Motor Vehicle Safety Standard No. 108 *Lamps, Reflective Devices, and Associated Equipment*.; Figure 10 of Standard No. 108 establishes the minimum desig photometrics for center high mounted stoplamps. The test procedure for this particular part of Standard No. 108 which is specified in SAE J186a, stipulates that the 'lamp axis shall be taken as the horizontal line through the light source.' However, I believe that you have misinterpreted the light cone that is involved. The pertinent light cone in this case has its vertex at the photometer and a cross section at the plane of the lamp which encompasses the lens areas. From Drawing A that you have provided, it appears that your rail would interfere with this light cone.; In order to determine if your rack interferes with the photometri requirements, the vehicle must be tested with the rack in position as installed on the vehicle. As the agency has noted before, the photometric requirements do not specify that the entire lens must be visible from each 5 degree down test point. Instead, they specify the intensity of light that must be visible from those points. Therefore, the requirement can be met with a lamp whose lens is partially obscured by a portion of the vehicle when viewed from some of the test points.; We hope that his interpretation is helpful to you. Sincerely, Frank Berndt, Chief Counsel