Mr. Dennis G. Moore
Sierra Products, Inc.
1113 Greenville Road
Livermore, CA 94550

Dear Mr. Moore:

This responds to your letter of July 31, 1995, on the subject of "optical combination" as that term is used in Motor Vehicle Safety Standard No. 108.

You enclosed a copy of a letter sent to you from this Office on March 4, 1977, and refer to a "Rider" in "a proposed change [around 1990] that had no relevance to this subject, whereas the Rulemakers added the expression, `NOT TO SHARE THE SAME HOUSING.'" You ask how "[u]sing the Scientific Argument and discussions I submitted back in 1975, 1976, and 1977, and the Re- Interpretation letter sent me, how can NHTSA support the SAME HOUSING definition they currently support."

You are talking of events of 18 to 20 years ago that are no longer relevant today. The definition that NHTSA supports contains no reference to lamp housings. Standard No. 108 was amended four years ago, in 1991, to clarify that the term "optical combination" is to be interpreted as defined by SAE Information Report J387 Terminology - Motor Vehicle Lighting NOV87. Under the SAE definition, optical combination results when a lamp "has two or more separate light sources, or a single light source that operates in different ways (e.g., a two-filament bulb)", and when "its optically functional lens area is wholly or partially common to two or more lamp functions." It is immaterial to this definition whether the light sources are in the same or different housings. I enclose a copy of a rulemaking proposal and final rules dealing with this issue that were published on November 6 and 8, 1990, and June 7 and November 7, 1991.

If you have further questions, you may refer them to Taylor Vinson of this Office by FAX (202-366-3820).


John Womack Acting Chief Counsel

Enclosures ref:108 d:9/25/95