Mr. William A. Parkyn
Teledyne Lighting & Display Products
12525 Daphne Avenue
Hawthorne, CA 90250

Dear Mr. Parkyn:

This is in reply to your letter of March 20, 1998, asking for an interpretation of Federal Motor Vehicle Safety Standard No. 108 with respect to stop lamps for motor-driven cycles.

Paragraph S5.1.1.22 of Standard No. 108 states in pertinent part that a motor-driven cycle may be equipped with a stop lamp whose photometric output "for the group of test points specified in Figure 1 is at least one-half of the minimum values set forth in that figure." Table III specifies that motorcycle stop lamps shall meet SAE Standard J586. You ask for confirmation that S5.1.1.22 "means that motor-driven cycle stop lamps must meet one half of the minima set forth in SAE Standard J586."

The minimum allowable candlepower value for a stop lamp is established by Figure 1b. For a single compartment stop lamp, this is 80 candlepower. Rather than determining photometric compliance through measuring candlepower at each individual test point, Figure 1c groups the individual test points into five Zones. Figure 1c is titled "Sum of the Percentages of Grouped Minimum Candlepower." The sum of the percentages for Zones 1 and 5 is 65 percent. The minimum allowable candlepower value for Zones 1 and 5 is determined by multiplying the minimum value of Figure 1b by the Zone percentage in Figure 1c, that is to say 65 percent of 80 candlepower, which is 52 candlepower. Under S5.1.122, then, at least half this value must be met by a motorcycle stop lamp, that is to say, Zones 1 and 5 must achieve at least 26 candlepower. The corresponding value established by SAE J586 is only 25 candlepower. For this reason, it is not correct to say that S5.1.1.22 means that motor-driven cycle stop lamps must meet one-half the minima set forth in SAE J586. However, this is a true statement for Zones 2, 3, and 4 where the values under both Figure 1 and SAE J586 are 100, 380, and 100 candlepower respectively.

In our review of your letter, we find that S5.1.1.22 could be more clearly expressed, and should read that the "photometric output for any group of test points specified in Figure 1c is at least one-half of the minimum value obtained when the minimum allowable stop lamp candlepower value of Figure 1b is multiplied by the appropriate percentage for the group that is specified in Figure 1c."

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.6/1/98