Interpretation ID: nht78-2.17

DATE: 06/08/78

FROM: AUTHOR UNAVAILABLE; J. J. Levin, Jr.; NHTSA

TO: Chrysler Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letter of May 4, 1978, to Howard Dugoff requesting confirmation of two interpretations of Motor Vehicle Safety Standard No. 108. You have cited our letter of December 29, 1976, to your Mr. Weil as support for your views.

With respect to your first concern, you have stated your understanding that in a multiple compartment taillamp the manufacturer has the option of using one or more compartments to meet the minimum photometric requirements specified for taillamps, but when the intensity ratio of the turn signal lamp to the taillamp is computed, the ratio must be determined with all taillamp compartments lighted.

As we interpret Standard No. 108's requirements for taillamps (SAE Standard J585d, Tail Lamps (Rear Position Light), August 1970), a single compartment lamp may be used as a taillamp, but if a multiple compartment lamp or multiple lamps are used to meet the photometric requirements, S3.1 of J585d requires that the combination of the compartments or lamps must be used to meet the photometric requirements for the corresponding numbers of lighted sections (Table 1, J585d) in those instances where the distances between filament centers do not exceed 22 inches for two-compartment or lamp arrangements, and 16 inches for three compartment or lamp arrangements. If these distances are exceeded, each compartment or lamp must comply with the photometric requirements for one lighted section. Therefore your interpretation is incorrect that a manufacturer may use only one compartment of a multi-compartment lamp when considering compliance with the photometric requirement for taillamps.

Your second concern is the requirement for multiple lamps in excess of three. You have noted that Table 1 of SAE J585 makes no provision for candlepower requirements where there are more than three lighted sections. Noting that the maximum candlepower permissible rises in increments of 5 per section (15 for one section, 20 for two sections, 25 for three sections) you have asked for confirmation of your opinion that "it appears logical that the allowable candlepower for a four compartment system should be 30 candlepower."

Standard No. 108 does not specify requirements for compartments or lamps in excess of three. If you wish to use a four compartment or lamp system you are legally free to distribute the candlepower as you deem appropriate. Accordingly we have no objection to your belief that 30 candlepower is allowable provided that the multiple compartment lamp or multiple lamp arrangement meets all other requirements of J585d.

SINCERELY,

CHRYSLER CORPORTION May 4, 1978

Howard Dugoff Deputy Administrator National Highway Traffic Safety Administration

Dear Mr. Dugoff:

Re: MVSS 108 - Requirements for Multiple Cavity Tail Lamps or Multiple Tail Lamps

The NHTSA provided interpretations of certain requirements of MVSS No. 108 as applied to photometric test requirements for multiple cavity and multiple lamp configurations in a letter of December 29, 1976. Our further review of MVSS No. 108 has uncovered two additional points pertaining to tail lamps on which we would appreciate your advice.

I. Photometric Requirements

MVSS No. 108 incorporates by reference SAE Recommended Practice J585d which specifies the photometric requirements for tail lamps. Paragraph 3.1 of SAE J585d provides that multiple compartment lamps (or multiple lamps) may be used to meet the photometric requirements for a tail lamp. Additionally, paragraph 3.1 describes how multiple compartments or multiple lamps are to be treated if they are in fact used to meet the photometric requirements for a tail lamp.

Our understanding of these requirements is that the manufacturer has the option to use one or more compartments of a multi-compartment lamp (or one or more lamps of a multiple lamp system) to meet the photometric requirements specified. In cases where the manufacturer uses only one compartment of the lamp to meet the photometric requirements for a tail lamp, compartments or lamps not used are considered as "supplemental lamps" and are not required to meet test requirements except for the differential values discussed in the next paragraph.

The above is consistent with your letter of December 29, 1976 that stated that the NHTSA interprets MVSS No. 108 as requiring that the ratio of the turn signal lamp to the tail lamps must be computed with all the lamps lighted when multiple compartment and multiple lamp configurations are used. Such a requirement, of course, maintains the differentiation between the turn signal and the tail lamps.

The net result of the above as we interpret the regulation is that where there is a multiple compartment tail lamp (or where there are multiple tail lamps) it is necessary to measure the output of all tail lamps in determining the ratio between tail lamp intensity and turn signal intensity. However, it is permissible to use only one compartment of a multi-compartment lamp (or one lamp from a multiple lamp system) when considering compliance with the photometric requirements for tail lamps; other lamps or compartments would be merely "supplemental."

II. Multiple Lamps in Excess of Three

Section 3.1 of SAE J585d further provides that if one or more lamps of a multiple compartment lamp (or multiple lamps) is used to meet the prescribed photometric requirements for tail lamps the maximum candlepower for the combination of all the compartments (or lamps) must not exceed those set forth in Table 1 of SAE J585d for the corresponding number of lighted sections. The candlepower values specified in Table 1 are 15 for a one lighted section, 20 for two lighted sections, and 25 for three lighted sections. Use of lamps with four or more compartments or lamps are not prohibited. However, the Table does not contain a progression of maximum candlepower values for lamps with additional compartments beyond three. While not specified in the standard, in keeping with the progression of higher values in the Table for one, two, and three compartment lamps, i.e., 15, 20, and 25 candlepower, it appears logical that the allowable candlepower for a four compartment system should be 30 candlepower.

We would appreciate your confirmation of our interpretation of these provisions of MVSS No. 108 set forth in Section I and Section II above.

Thank you for your assistance.

R. O. Sornson Manager Environmental Relations