Interpretation ID: 2953o
DOT Paperwork Processor
234l7 Everett Place
Ramona, CA 92065
Dear Mr. Ziolo:
This is in reply to your letter of April 20, 1988, asking about the acceptability under Safety Standard No. l08 of modifying imported vehicles so that they are equipped with two Type 2D1 and two Type 1C1 headlamps. You have been informed by the agency's Office of Vehicle Safety Compliance that this is impermissible "because they are 'nonconforming' 'headlight systems'." You disagree because you believe that the minimum requirements of the Standard are satisfied by the Type 2D1 lamps, and that "S4.4 appears to permit such a combination."
Paragraph S4.4 is not applicable to the situation you present as it refers to combinations of lamps serving different functions; in your discussion, the lamps serve the identical function of headlighting. Given the fact that the Type 2D1 sealed beam 7" diameter headlamps fulfill the headlighting requirements of the Standard, your question must be viewed as whether a supplement to the headlighting system is permissible under Standard No. l08.
Paragraph S4.l.3 of Standard No. l08 permits the addition of nonrequired lighting equipment provided it does not impair the effectiveness of the equipment that the standard requires. The two Type 1C1 5 3/4" diameter sealed beam lamps in a four lamp headlighting system form the major portion of an upper beam headlighting system. The two Type 2D1 lamps in a two lamp headlighting system form the whole of an upper beam headlighting system. Thus, a vehicle furnished with the systems you posit would be equipped with more than one upper beam headlighting system. The Type 2D1 system must be designed to conform to the photometric requirements of SAE Standard J579c DEC79 "Sealed Beam Headlamp Units for Motor Vehicles." The SAE Standard establishes at two test points, H-V and 4 D-V, maximum allowable candela of 75,000 and 5,000 respectively for each Type 2D1 headlamp. This means that the maximum allowable candela for headlighting systems at these test points is 150,000 and l0,000 candela. The Type 1C1 headlamps will also be designed to conform to SAE J579c. Corresponding maxima at test points H-V and 4 D-V for Type 1C1 systems are 60,000 and 5,000. Thus, a vehicle equipped with the lamps you have described could emit a total of 270,000 candela at test point H-V (when only 150,000 is permitted), and 20,000 at 4D-V (when only l0,000 is allowable).
Agency research has shown that candela readings in excess of 150,000 greatly increase the potential for glare with little increase in seeing ability. This glare would be visible both to the driver of an oncoming car, and the driver of the modified vehicle itself through creation of a "veiling" glare. The addition of the Type 1C1 headlamps would therefore impair the effectiveness of the Type 2D1 headlighting system, and is forbidden by S4.1.3.
We appreciate your interest in safety.
Sincerely,
Erika Z. Jones Chief Counsel
ref:108 d:9/12/88