Mr. Kiminori Hyodo
Deputy General Manager, Regulation & Certification
Koito Manufacturing Co., Ltd.
Dear Mr. Hyodo:
This responds to your letter, in which you ask about the relative location of the lower and upper beam light sources under Federal Motor Vehicle Safety Standard (FMVSS) No. 108, Lamps, Reflective Devices, and Associated Equipment. Specifically, you ask if the optical axis, as defined by the manufacturer, can be used to determine the relative location of the lower beam light source to that of the upper beam headlamp. As discussed below, our answer is yes. It is our opinion that for purposes of visual/optically aimed headlamps, the point where the optical axis intersects the lens of the headlamp (as determined by the manufacturer) is the reference point used for purposes of determining the relative location of the beams.
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). NHTSA does not provide approvals of motor vehicles or motor vehicle equipment. Instead, manufacturers are required to self-certify that their products conform to all applicable safety standards that are in effect on the date of manufacture. NHTSA selects a sampling of new vehicles and equipment each year to determine their compliance with applicable FMVSSs. If our testing or examination reveals an apparent noncompliance, we may require the manufacturer to remedy the noncompliance, and may initiate an enforcement proceeding if necessary to ensure that the manufacturer takes appropriate action.
The relative locations of lower and upper beam headlamps is governed under paragraphs S7.4(b) and S7.5(d)(2) of FMVSS No. 108. These paragraphs read, respectively:
S7.4 * * *
(b) The lower and upper beams shall be provided only as follows where each headlamp contains two light sources:
(1) The lower beam shall be provided either by the most outboard light source (or the uppermost if arranged vertically), or by all light sources.
(2) The upper beam shall be provided either by the most inboard light source (or the lowermost if arranged vertically), or by all light sources.
* * * *
S7.5(d) For a headlamp equipped with dual filament replaceable light sources, the following requirements apply:
* * * *
(2) The lower and upper beams of a headlamp system consisting of two lamps, each containing either one or two replaceable light sources, shall be provided as follows:
(i) The lower beam shall be provided in one of the following ways:
(A) By the outboard light source (or upper one if arranged vertically) designed to conform to:
(1) The lower beam requirements of Figure 27-1 or Figure 27-2, or Figure 17-1 or Figure 17-2, if the light sources in the headlamp system are any combination of dual filament replaceable light sources other than Type HB2; or
(2) The lower beam requirements of Figure 17-1 or Figure 17-2, if the light sources are Type HB2, or any dual filament replaceable light sources that include Type HB2; or
(B) By both light sources in the headlamp, designed to conform to the lower beam requirements specified above.
(ii) The upper beam shall be provided in one of the following ways:
(A) By the inboard light source (or the lower one if arranged vertically) designed to conform to:
(1) The upper beam requirements of Figure 27-1 or Figure 27-2, or Figure 17-1 or Figure 17-2, if the light sources in the headlamp system are any combination of dual filament replaceable light sources other than Type HB2; or
(2) The upper beam requirements of Figure 17-1 or Figure 17-2, if the light sources are Type HB2, or any dual filament replaceable light sources that include Type HB2; or
(B) By both light sources in the headlamp, designed to conform to the upper beam requirements specified above.
We note that the specifications described in paragraphs S7.4(b) and S7.5(d)(2) were originally adopted in the 1970s to apply to four-lamp sealed beam headlighting systems in which each lamp was identical in size and contained only a single light source. When the lamps were mounted horizontally, side by side with identical horizontal centerlines, the outboard lamps were required to be the ones providing the lower beam, which also served to mark the width of the vehicle. When the lamps were mounted vertically, one atop the other with identical vertical centerlines, the lower beam continued to mark the width of the vehicle, but it was required to be the uppermost headlamp in order to provide a greater seeing distance. This established the location priority for the lower beam, that it be the outermost beam, and uppermost beam if the vertical axes of the lamps coincided.
As you are aware, in our previous letter of interpretation to you, we stated that manufacturers could use their discretion when specifying the location of the optical axis. We noted that for visual/optically aimed headlamps, the term optical axis as used in FMVSS No. 108 refers to the reference axis (a.k.a. mechanical axis) of the headlamp. We said that because we believe, given the asymmetric nature of modern headlighting systems, the output of a lamp comprised of multiple sources is not in a pre-defined position (such as at the geometric center of the lens), as it is with symmetrical lamps such as turn signals. In these cases, the manufacturer is the entity best positioned to locate the reference axis from which photometric output of the the beam will be measured. NHTSA stated that it will use that reference axis when doing its own testing.
For similar reasons, with these kinds of lamps, we believe that the same reference axis (i.e., the optical axis) that is used to align the beam when measuring the photometric output of the lamp is also useful for determining the reference point for the physical location of the lens. As stated above, the purpose of the specifications at issue is to establish the location priority of the lower beam. The optical axis, as defined by the manufacturer, is already used to determine the optical center of the light beam produced. Therefore, as long as the reference axis of the lower beam headlamp is located farther outboard than the reference axis of the upper beam (or uppermost if arranged vertically), such alignment would be permissible under Standard No. 108.
If you have any further questions, please contact Ari Scott of my staff at (202) 366-2992.
Anthony M. Cooke