Interpretation ID: nht90-4.60

TYPE: Interpretation-NHTSA

DATE: November 13, 1990

FROM: M. Iwase -- General Manager, Technical Administration Dept., Koito Manufacturing Company

TO: Paul Jackson Rice -- Chief Counsel, NHTSA

TITLE: Re FMVSS No. 108 (Lamp, reflective devices, and associated equipment) Photometric Measurement Procedures for L.E.D. CHMSL

ATTACHMT: Attached to letter dated 12-17-90 to M. Iwase from Paul Jackson Rice (A37; Std. 108)

TEXT:

We would hereby ask you to provide us with your kind advice concerning photometric measurement procedures for L.E.D. center high-mounted stop lamps (CHMSL).

Photometric output of L.E.D. lighting device decreases as the time passes after activation, as shown in Figure 1. This is caused by the thermal characteristic of L.E.D. discrete itself. Our question is about the timing of photometry when the photometri c output of L.E.D. CHMSL should be measured for the verification of compliance with the photometric requirements of FMVSS No. 108. It is reasonable that it shall be measured when 5 minutes has elapsed after the lamp is energized, with the following reas ons, we think;

(1) Our real-car field test has been performed to see how often and how long foot brake application (stop lamp operation) is raised during actual driving in the certain urban area. As the result of our field test, it was found that the c ontinuance is for 5 minutes at best for our brake application (refer to Figure 2).

(2) Section 3.1.5.3 "Photometric Minumums" in SAE J1889 JUN88 specifies, as follows;

Photometric Minumums: For measurements to photometric minimum requiments, the test "device light output shall first be stabilized by energizing the device at laboratory ambient temperature (23 +/- 5 degrees C) until either internal he at builtup saturation has occured or 30 minutes has elapsed, whichever occurs first.

This provision is true of steady burn lamps, for example tail lamp, parking lamp, etc., however not true of stop lamp which is energized during just the period of service brake operation.

(3) S4.8 "Warpage Test on Devices with Plastic Components" and Table 1 "Cycle Time (Min)" in SAE J575 JUL83 specifies 5-on/5-off operating cycle for stop lamps.

Whether could our interpretation above-mentioned be legally accepted? Upon your kind review, your prompt reply would be highly appreciated.

Attachment

Figure 1. Photometric Output Of L.E.D. And Incandescent Bulb (Graph Omitted) Figure 2. Brake Application Period (Graph Omitted) Test Method: Three (3) vehicles (A, B and C) chosen at random were chased and measured brake application periods. Date: January 10, 1990 Location: Urban area (in Nagoya city)

Remark: Each test data of three vehicles is continuous, namely Vehicle A was measured the brake application for 72 minutes, and Vehicle B and C were measured for 24 minutes, respectively.