Interpretation ID: aiam2515
Executive Vice President
Wesbar Corporation
Box 577
West Bend
WI 53095;
Dear Mr. Weber: Thank you for your frank letter of January 13, 1977, commenting upo the lack of clarity you feel exists in my letter to you of December 6, 1976, interpreting Motor Vehicle Safety Standard No. 108.; As a lawyer it is obvious to me that the best regulatory practice is t be as specific as possible in establishing requirements and prohibitions. When a regulation itself is unclear, however, its interpretation may necessarily be imprecise. Because the term 'optical combination' in S4.4.1 is not defined, my answers were necessarily worded in general terms though with the thought of establishing a general framework of guidance for you. They were not intended to be 'a masterpiece of bureaucratic weasel words.' My letter meant, in plain English, that where tail lamps and clearance lamps are in a single compartment we don't want one lamp to perform, or to be perceived as performing, the function of the other. It is evident from your letter and others that our previous interpretations of the term 'optical combination' have been found to be ambiguous and lacking in the objective criteria that a Federal motor vehicle safety standard must provide. We have reviewed the matter, and now wish to modify our previous interpretation. In our view a lamp is 'optically combined' when the same light source (i.e. bulb) and the same lens area fulfill two or more functions (*e.g.* taillamp and stop lamp, clearance lamp and turn signal lamp). A dual filament bulb would be regarded as the 'same light source'. In determining conformance, the photometric requirements for clearance and taillamp functions, where two bulbs are located in a single compartment, must be met with only the bulb energized that is designed to perform the specific function. But the 15 candlepower maximum under Standard No. 108, however, would be determined with both the taillamp and clearance lamp bulb energized. Further, the lamp must be located to meet requirements for both clearance and taillamps. Our re- interpretation means that the issue of light spill-over from one area of the lamp to another is irrelevant to conformance.; Sincerely, Frank Berndt, Acting Chief Counsel