Mr. Lance Tunick
Vehicle Science Corporation
P.O. Box 1015
Golden, CO 80402-1015

Dear Mr. Tunick:

This is in reply to your letter of April 14, 1995, to Taylor Vinson of this Office asking for an interpretation of Motor Vehicle Safety Standard No. 108.

Specifically, you are concerned with the meaning of the words "outer lens surface" that appear in SAE Standard J586 Stop Lamps for use on Motor Vehicles Less Than 2032 mm in Overall Width FEB84, an SAE standard incorporated by reference in Standard No. 108. These words appear as part of the visibility specifications under the installation requirements. You point out that "outer lens surface" as not been defined either by the SAE or by NHTSA. You believe that the phrase within the context of SAE J586 can mean "light emitting surface" as defined in SAE J387, and ask for confirmation.

According to Standard No. 108 (SAE J586), "to be considered visible, the lamp must provide an unobstructed view of the outer lens surface of at least 12.5 square centimeters measured at 45 degrees to the longitudinal axis of the vehicle." SAE Information Report J387 Terminology - Motor Vehicle Lighting OCT88 defines "light emitting surface" as "all or part of the exterior surface of the transparent or translucent lens that encloses the lighting or light signalling device and allows conformance with photometric and calorimetric requirements."

We believe that it would be appropriate to substitute the definition of "light emitting surface" for "outer lens surface" in SAE J586. The "outer lens surface" of J586 appears to mean the same as "the exterior surface of the

transparent or translucent lens" of J387. Thus, stop lamp visibility conformance would require an unobstructed view of the light emitting surface of at least 12.5 square centimeters.

As always, Taylor will be happy to answer any further questions you may have on this matter (202-366-5263).

Sincerely,

John Womack Acting Chief Counsel ref:108 d:5/3/95 9