Reitter & Schefenacker GmbH & Co KG
Dear Herr Sandig:
This responds to your FAX of June 6, 1994, to Mr. Van Iderstine of this agency, asking for an interpretation of Motor Vehicle Safety Standard No. 108.
You present a drawing of a rear combination lamp incorporating one stop lamp and two taillamps. You have asked whether it is "necessary that we must have the ratio 5:1/3:1 between the stop and the tail lamp measurements in this arrangement?"
If the lamp is intended for use on narrower vehicles, the answer depends upon the distance between the optical axes of the stop and taillamp functions. SAE Standard J586 FEB84 Stop Lamps for Use on Motor Vehicles Less Than 2032 mm in Overall Width is incorporated by reference in Standard No. 108. Paragraph 188.8.131.52 of J586 is the source of the ratio: "[w]hen a tail lamp is combined with the stop lamp, the stop lamp shall not be less than three times the luminous intensity of the tail lamp at any test point; except that at H-V, H-5L, H-5R, and 5U-V, the stop lamp shall not be less than five times the luminous intensity of the tail lamp." However, in a multiple compartment lamp such as yours, if "the distance between optical axes for one of the functions exceeds the dimensions specified in paragraph 184.108.40.206 [i.e., 560 mm] the ratio shall be computed for only those compartments or lamps where the tail lamp and stop lamp are optically combined." Although your combination lamp design combines the two functions, your drawing indicates that they are not optically combined, and the ratio will not apply if the optical axes are more than 560 mm apart. The ratio will apply if the distance between the optical axis of the stop lamp and that of either taillamp is 560 mm or less.
SAE Standard J1398 MAY85 Stop Lamps for Use on Motor Vehicles 2032 mm or More in Overall Width is the standard incorporated in Standard No. 108 that applies to lamps used on wider
vehicles. Its paragraph 220.127.116.11 establishes the same 5:3 ratio (though not including H-5L in the five times ratio), but does not provide an exception based upon spacing of optical axes. Thus, if your lamp is designed for wider vehicles, the ratio applies regardless of the spacing of the optical axes.
John Womack Acting Chief Counsel ref:108 7/6/94