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 recent letter requesting further clarification of our August 1, 2005, letter of interpretation to Mr. Takayuki Amma of Koito Manufacturing Co. (Koito), in which we stated that your company’s proposed intensity-reducing headlamps would not meet the "steady-burning" requirement of S5.5.10 of Federal Motor Vehicle Safety Standard (FMVSS) No. 108, Lamps, Reflective Devices, and Associated Equipment. As described in Koito’s earlier letter, the proposed headlamp would automatically and perceptibly reduce intensity (with approximately a 20-40% reduction in wattage) when the vehicle is stopped, thereafter returning to full intensity once vehicle motion resumed. Your latest letter asked whether a headlamp would be permitted to change in intensity, so long as the light is "perceived to be a steady beam and essentially unvarying in intensity, as well as occurring gradually (e.g. by setting some phase period) such that the change would not be perceptible to oncoming drivers". Presuming that this new design, consistent with your earlier design, would be such that "[a]t all times through the change of the intensity, the lamps provide sufficient level of intensity and will be within the parameters of the minimum and maximum values of candela specified in FMVSS No. 108," the answer to your question is yes.

    To reiterate the relevant provision of FMVSS No. 108, paragraph S5.5.10 provides:

    In short, S5.5.10(d) of FMVSS No. 108 requires that all lamps must be "steady burning," unless otherwise permitted, and while S5.5.10(b) does permit headlamps to be wired to flash for signaling purposes, we note that paragraph S3 of FMVSS No. 108 defines "flash" as meaning "a cycle of activation and deactivation of a lamp by automatic means…." Through our interpretations, we have explained that the "steady-burning" requirement under the standard means "a light that is essentially unvarying in intensity" (see e.g. , February 9, 1982, letter of interpretation to Dr. H.A. Kendall).

    We further clarified the requirement in S5.5.10(d) in our March 10, 1994 letter of interpretation to Mr. Joe de Sousa. That letter involved the permissibility of daytime running lamps (DRLs) that operated by using the vehicle’s lower beam headlamps at less than full intensity through "pulse width modulation," a technique which cycles the headlamps "on and off faster than the eye can detect". In our response to Mr. de Sousa, we stated that although a modulating headlamp technically is not a steady-burning one, for purposes of this requirement under S5.5.10(d), we have concluded that there is no failure to conform if the modulating light from the lamp is perceived to be "steady-burning. "

    In our July 21, 1998, letter of interpretation to Mr. Ian Goldstein, we stated that "gradational" daytime running lamps (DRLs), devices that are capable of modulating the intensity of the DRLs according to ambient light conditions, are permissible under FMVSS No. 108. In that letter, we stated, "A DRL with a gradational feature would continue to provide the steady-burning light that is required for DRLs. The standard does not prohibit changes in intensity, which we presume will be within the parameters of the minimum and maximum values of candela specified. "

    In sum, if an intensity-reducing headlamp operates in a manner that meets all of the other applicable requirements of the standard and is perceived as being steady-burning, we believe that such a design would be permissible under the standard, and we would not expect it to be a source of distraction to other drivers.

    If you have further questions, please feel free to contact Eric Stas of my staff at this address or by telephone at (202) 366-2992.


    Stephen P. Wood
    Acting Chief Counsel