Interpretation ID: 20127.ztv

Mr. Tom Shreeve
Manager of Engineering
Trident Automotive Lighting
P.O. Box 821
Kentwood, MI 49518-0821

Dear Mr. Shreeve:

This is in reply to your letter of June 7, 1999, asking for an interpretation of S5.1.1.18 of Federal Motor Vehicle Safety Standard No. 108, as modified by footnote 1 of Figure 2.

Table I and Table III of Standard No. 108 require motor vehicles as specified in these Tables to be equipped with a backup lamp complying with SAE Standard J593c Backup Lamps February 1968. However, under S5.1.1.18, a backup lamp is not required to meet the minimum photometric values at each test point specified in Table 1 of SAE J593c if the sum of the candlepower actually measured at the test points within a group listed in Figure 2 of Standard No. 108 is not less than the sum of the total minimum candlepower specified in Figure 2 for test points in that group.

Figure 2 specifies minimum luminous intensity for backup lamps for five groups of test points, or "zones" as you refer to them. Both J593c and Standard No. 108 permit more than one backup lamp to be used. Footnote 1 of Figure 2 states that:

When 2 lamps of the same or symmetrically opposite design are used, the reading along the vertical axis and the averages of the readings for the same angles left and right of vertical for 1 lamp shall be used to determine compliance with the requirements. If 2 lamps of differing designs are used, they shall be tested individually and the values added to determine that the combined units meet twice the candela requirements.

When only 1 backup lamp is used on the vehicle, it shall be tested to twice the candela requirements.

You interpret this as meaning that,

when using two lamps that are symmetrically opposite in design, the intent of this footnote was to allow the average of the two lamps combined output. That is, the right hand lamp output in zone 2 added with the left hand lamp output in that same zone 2, and that the average of those two lamps for that zone must not be less than the minimum candela requirements.

However, your customer thinks that

the intent is for us to average the zones 2 and 5 of the same lamp. If this is done, it is measuring output of the lamp at angles opposite of each other and that these two zones actually are intended to illuminate a completely different target area. If the averaging is done in this manner, it will also default the third sentence of the footnote [which reads: "When only one backup lamp is used on the vehicle, it shall be tested to twice the candela requirements."].

SAE Standard J593c is straight-forward. If a single backup lamp is used, it shall comply with twice the minimum candela requirements specified in Table 1 of J593c. If two lamps are used (and they are identical or symmetrical), each lamp must meet the minimum candela requirements. Thus, the total light output of a backup lamp system is intended to be roughly the same, whether the system consists of one or two lamps. This is the basic backup lamp requirement incorporated by reference in Standard No. 108.

Unlike SAE J593c and as an alternative to it, S5.1.1.18 does not require a lamp to meet every test point if the sum of the candlepower measured for all test points within a group of test points described in Figure 2 is not less than the sum of the minimum candlepower required for all test points in that group.

The question that you have asked is how Footnote 1 shall be interpreted as to group photometric measurements in a backup lamp system consisting of two symmetrically opposite lamps. This requires an interpretation of the meaning of "the averages of the readings for the same angles left and right of vertical for 1 lamp shall be used to determine compliance with the requirements." We did not intend Footnote 1 to alter the concept of group photometrics. The quoted language simply means that each lamp shall meet the group candlepower minimum specified in Figure 2 for each group. It does not mean, as your customer thinks, that two groups within the same lamp left and right of vertical are combined into a larger group and averaged. The footnote deals solely with individual test points.

Footnote 1 clearly refers to a single lamp and not, as you argue, to the average of the output of the same group in two lamps, one on each side of the vehicle. We interpret it as saying that, if two lamps of the same or symmetrically opposite design are to be installed, the test for a single lamp in a pair shall be as follows. First, measure all test points. Second, take the values of the test points on the vertical axis and use them to calculate their respective group totals. Next, add the measured values of two symmetrically opposite test points, divide by two, and use this average as the value for each of the two test points when calculating the group sum in which each of the two test points is located. Then do the same for the rest of the test points. Finally, calculate the sum of each group and compare with the totals provided in Figure 2 for each group to determine whether the lamp meets the test requirements of Standard No. 108.

If you have any questions, you may call Taylor Vinson of this Office (202-366-5263).

Sincerely,
Frank Seales, Jr.
Chief Counsel
ref:108
d.10/26/99