Interpretation ID: nht76-2.30

DATE: 12/06/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Wesbar Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letter of October 28, 1976, asking several questions with respect to that portion of paragraph S4.4.1 of Motor Vehicle Safety Standard No. 108 which prohibits the optical combination of clearance and tail lamps. You have also expressed your concern, in a recent telephone conversation with Mr. Vinson of my staff, about the ACUTEK interpretation of October 22, 1976, to be discussed below.

The distinction between the hypothetical lamp in Question 2 of your letter of September 7, 1976, and the Acutek lamp is that there is no opaque barrier wall in the former, separating the tail lamp bulb and the clearance lamp bulb, while in the latter the barrier rises to the base of the bulb. Since Standard No. 108 does not require separate compartments (i.e., an opaque barrier) for tail lamps and clearance lamps, it is obvious that the prohibition against optical combination means that (a) a single bulb may not perform both functions and (b) a single bulb must not be perceived as performing both functions. This was the rationale behind Mr. Driver's advice to Acutek that the available data indicated "that when the tail lamp bulb [on the Acutek lamp] is activated independently from the clearance lamp bulb, and vice versa, there is no appreciable amount of incidental light emitted from the lens of the clearance lamp," and that "the amount of light 'spill' appears to be so small that it would not be interpreted (by a driver following the vehicle on which it is installed) as illuminating the lens of the tail lamp when operated in the clearance lamp mode, and vice versa."

If you apply this general principle to the questions you asked then I think you will have the answers. The principle is necessarily dependent upon the candlepower output of any lamp to which it is applied, a value not given in your questions. Thus, the principle cannot be quantified and the determination of the extent of light spill is necessarily subjective, and certification is dependent upon a manufacturer's good faith in attempting to achieve compliance.

After reviewing this matter I must admit that I am curious as to the safety rationale behind the prohibition. Paragraph S4.4.1 had its genesis in a similar provision in Bureau of Motor Carrier Safety regulations (49 CFR 393.22(b)(3), formerly 393.22(c)) and was adopted in conformance with it. The Society of Automotive Engineers, however, does not prohibit combining these lamps. If clearance lamps are mounted below 72 inches -- the maximum allowable mounting height for tail lamps -- it may be that they could be combined with tail lamps, without any detriment to safety, and at a saving to the consumer. Perhaps you would like to comment on this.

SINCERELY,

WESBAR CORPORATION

October 28, 1976 Frank Berndt

Acting Chief Counsel

U.S. Dept. of Transportation

National Highway Traffic Safety Administration

Refer: N40-30

1. Thank you for your October 7, 1976 response to our inquiries. Your answers have clarified several grey areas of various manufacturers interpretations of S 4.4.1 of DOT 108.

2. There is one further design on which we would ask for your interpretation in regard to the combination of clearance lamp and tail lamp in approximately the same cell.

3. Your response (paragraph 2 of your letter) to our question: "Can a clearance lamp and tail lamp be combined in a single compartment with no opaque barrier wall existing between the clearance lamp and tail lamp bulb?" was concise and direct but it left one consideration unanswered. Your reply was directed to a lamp which had one lens serving both functions and no opaque barrier between the tail lamp and clearance lamp bulbs respectively.

4. We now ask your interpretation of S 4.4.1 as it would apply to a combination lamp designed as follows:

1. Only a partial partition exists between the clearance lamp and tail lamp compartments.

2. There are separate lenses for clearance and tail lamp functions (though contiguous).

3. The tail lamp partially illuminates the clearance lamp compartment and lens.

4. The clearance lamp partially illuminates the tail lamp compartment and lens.

5. The turn signal filament, when flashing illuminates both clearance and tail light lenses and compartments.

5. Based on your interpretation contained in paragraph 2 of your letter, we believe this lamp would not be approved since the lamps designated for each separate function would illuminate the individual lenses of each function.

6. However, we would prefer not to accept our own interpretation of this design but rather have you give us an NHTSA official interpretation to the following questions:

a. Would a lamp with the design features described in paragraph 5 be approved under S 4.4.1?

b. Does, in fact, the clearance lamp have to be totally isolated in a separate compartment from the tail lamp so that no light from the tail lamp bulb illuminates the clearance lamp lens?

c. Does the fact that there are separate lenses, contiguous to one another, change your interpretation as given in paragraph 2 of your October 7, 1976 letter since both lenses would be illuminated when both or either lamp is in use and, therefore, considered combined optically?

7. For your study and consideration we submit the attached sketch and photos of a model depiciting the conditions outlined in paragraph 5 of this letter.

Your early response will be appreciated.

B. R. Weber Executive Vice President

SIDE VIEW SHOWING RELATIVE POSITION OF CLEARANCE LAMP & TAIL LAMP NOT COMPLETELY ISOLATED FROM ONE ANOTHER

(Graphics omitted)

(LACK OF A FULL DIVIDING WALL PERMITS THE TAIL LIGHT BULB TO ILLUMINATE PART OF THE CLEARANCE LAMP COMPARTMENT AND CONVERSITY, THE CLEARANCE BULB ILLUMINATES PART OF THE TAIL LIGHT COMPARTMENT

(Graphics omitted)

(Graphics omitted)