Interpretation ID: 22938.ztv.wps

Mr. Tadashi Suzuki
Manager, Regulation & Homologation
Stanley Electric Co., Ltd.
2-9-13, Nakameguro, Meguro-ku
Tokyo 153-8636
Japan

Dear Mr. Suzuki:

This is in reply to your letter of March 22, 2001, asking for an interpretation of "the photometric ratio requirement of tail lamp and stop lamp" of Federal Motor Vehicle Safety Standard No. 108.

Standard No. 108 incorporates by reference SAE Standard J586 FEB84, Stop Lamps for Use on Motor Vehicles Less Than 2032 MM in Overall Width. You seek our advice on "limiting the compartments to be lit of both tail lamp and stop lamp when computing the photometric ratio of various types of arrangement." You have enclosed a drawing that shows several examples of lamp arrangements.

Example 1 depicts a two-compartment design, one a stop lamp, the other a taillamp. The distance between the filament centers of the light sources in the two compartments is 200 mm. You ask whether the photometric ratio should be applied in this case.

As you wrote, paragraph 5.1.5.3 of SAE J586 states, in pertinent part, "If a multiple compartment . . . arrangement is used and the distance between optical axis for both the tail lamp and stop lamp is within the dimensions specified in paragraph 5.1.5.2, the ratio of the stop lamp to the tail lamp shall be computed with all the compartments . . . lighted." The distance between adjacent light sources specified in 5.1.5.2 for a multiple compartment lamp is 560 mm or less. In your Example 1, the distance is 200 mm. Therefore, the ratio of the stop lamp to the taillamp in your Example 1 must be computed with both compartments lighted.

Example 2 also depicts a two compartment lamp, one of which serves as a taillamp and the other, both a taillamp and a stop lamp function. The distance between the filament centers of the light sources in the two compartments is 200 mm. You ask whether both compartments should be included "when applying the ratio requirement."

The answer is yes. Because one of the taillamps is combined with the stop lamp in the same compartment, as you note, paragraph 5.1.5.3 first establishes a ratio that must be met by the dual-

purpose light source in that compartment. Then, because the adjacent compartment also serves as a taillamp, and the distance between the optical centers of the two light sources is 200 mm, the ratio of the stop lamp to the taillamp in the adjacent compartment must be computed with both compartments lighted.

Example 3 depicts a three-compartment lamp. The first two compartments are taillamps and the filament centers of the light sources are 200 mm apart. The third compartment is the stop lamp; the filament center of its light source is 250 mm from that of the light source in the adjacent taillamp compartment. You ask whether the ratio requirement should be satisfied. If so, "what compartment should we use? All of the three compartments, or [only the stop lamp and adjacent taillamp compartments]?"

You should use all three compartments in satisfying the ratio requirement. Paragraph 5.1.5.2 does not apply the ratio requirement in a multiple compartment lamp if "the distance between adjacent light sources does not exceed . . .410 mm for three compartments." Although the distance between the light sources in the first and third compartments is 450 mm, the distance between the first and second adjacent light sources is only 200 mm, and the distance between the second and third adjacent light sources is only 250 mm. Therefore, the ratio still applies.

I hope that this answers your questions.

Sincerely,

John Womack
Acting Chief Counsel

ref:108
d.5/3/01