Interpretation ID: nht88-2.54

TYPE: INTERPRETATION-NHTSA

DATE: JUNE 22, 1988 EST

FROM: A. L. BRAGG -- LABORATORY MANAGER, TRUCK-LITE CO., INC.

TO: Z. TAYLOR VINSON -- SENIOR STAFF ATTY., NHTSA

TITLE: REQUEST FOR INTERPRETATION OF S4.1.16 AND S4.1.17 IN STANDARD NUMBER 108

ATTACHMT: LETTER DATED NOV. 3, 1988 (EST) TO A. L. BRAGG, LABORATORY MGR., TRUCK-LITE CO., INC., FROM ERIKA Z. JONES, CHIEF COUNSEL, NHTSA

TEXT: Our company currently manufactures several variations of stop, turn, and tail lamps that have a twelve square inch lens. Some particular models of this lamp also incorporate a ring of reflex reflector optics around the outside of the lens. It is our un derstanding that for the purposes of measuring the effective projected illuminated area of the lenses illuminated by an internal bulb, the reflex area (if present) must be subtracted from the total lens area, even though it may appear to transmit light. In the case of our particular lamps, we have a total of twelve square inches, from which we would subtract a four square inch area of reflex reflector which leaves eight square inches of effective projected illuminated lens area.

We note that the current FMVSS-108 document refers to SAE J586c, August 1970 for stop lamps and SAE J588e, September 1970 for turn signal lamps. A close reading of these standards indicates (to us at least) that for vehicles of eighty inches or more in width, an effective projected illuminated area of at least twelve square inches is required when two or more lamps are mounted closer together than twenty-two inches. We would further surmise that if a single stop/turn lamp were used or if two or mor e stop/turn lamps were used but that they were kept at least twenty-two inches or more apart, the twelve square inch rule would not be enforced and that eight square inches of effective projected illuminated area would be sufficient.

This matter is further complicated by the fact that in addition to the SAE standards just mentioned, there is a reference in S4.1.1.7 which seems to indicate that twelve square inches is required for vehicles ove eithty inches in overall width.

Our basic question is in reference to our combination lamp which has four square inches of reflector area and eight square inches of stop, tail and turn area. For vehicles over eighty inches wide can we advise our customers that these lamps may be us ed:

A) Singularly (that is one on each side of the vehicle in the rear) as a stop, turn, tail and reflex reflector?

B) In combination of two's or three's (on each side of the rear of the vehicle), provided that the lamps are separated by at least twenty-two inches?

We would be most grateful for your views and interpretation regarding the above. If we may offer any clarification, please feel free to contact us by letter or telephone.