Mr. Kiminori Hyodo

Deputy General Manager, Regulation & Certification

Koito Manufacturing Co., Ltd.

4-8-3, Takanawa

Minato-Ku Tokyo


Dear Mr. Hyodo:

This responds to your letter requesting clarification regarding the luminous intensity requirements for front turn signal lamps under Federal Motor Vehicle Safety Standard No. 108, Lamps, Reflective Devices, and Associated Equipment (FMVSS No. 108). Specifically, you asked whether the multiplier in paragraph S5.3.1.7 of Standard No. 108 applies to the minimum luminous intensities listed in Figure 20, Visibility of Installed Lighting Devices (Luminous Intensity Measurement Method). As discussed below, it does not.

By way of background, the National Highway Traffic Safety Administration (NHTSA) is authorized to issue FMVSSs that set performance requirements for new motor vehicles and items of motor vehicle equipment (see 49 U.S.C. Chapter 301). On August 11, 2004, NHTSA published a final rule updating FMVSS No. 108 to increase compatibility with the relevant standards of the Society of Automotive Engineers (SAE) and the Economic Commission for Europe (ECE) pertaining to a variety of lighting requirements (see 69 FR 48805).

The luminous intensity multiplier referred to in paragraph S5.3.1.7 of Standard No. 108 applies to the photometric requirements of turn signal lamps. Paragraph S5.3.1.7 specifies that the multiplier applied to obtain the required minimum luminous intensities shall be 2.5. The multiplier referred to in paragraph S5.3.1.7 supersedes the luminous intensity multiplier described in paragraph of SAE J588 (rev. Nov. 84), which has been incorporated by reference into FMVSS No. 108 via paragraph S5.1.1 and Table III of the standard. (S5.1.1 refers to Table III, which references SAE J588 (rev. Nov. 84) as the applicable standard for turn signal lamps.) To explain more fully, paragraph of SAE J588 (rev. Nov. 84) specifies numerous luminous intensity multipliers dependent on the lamp separation distance. Paragraph S5.3.1.7 overrides this SAE specification by requiring that turn signal lamps mounted within 100mm of the lighted edge of a headlamp shall use 2.5 as the multiplier. Thus, the luminous intensity multiplier referred to in FMVSS No. 108 paragraph S5.3.1.7 applies to the SAE J588 (rev. Nov. 84) photometric requirements of turn signal lamps.

We note that the minimum luminous intensities referred to in Figure 20 of FMVSS No. 108 are visibility requirements, not photometric requirements. The origin of these requirements is FMVSS No. 108 paragraph S5.3.2(b). This paragraph states that a manufacturer must certify compliance of each lamp to one of the following visibility requirement options, with one option being that each such lamp must provide a luminous intensity not less than that specified in Figure 20. Because this refers to visibility requirements, referencing the light seen by the human eye, as opposed to photometry requirements, referencing the output of light from the lamp (and which was the subject of the luminous intensity multiplier), the multiplier does not apply to the values in Figure 20.

I hope this information is helpful. If you have any further questions, please contact Ari Scott of my staff at (202) 366-2992.


Anthony M. Cooke

Chief Counsel