Interpretation ID: aiam4659
"W. Germany FAX Number 07121/35-1792 Dear Frau Schmock: This is i reply to your FAX of September 6, l989, to Mr. Van Iderstine of this agency, asking four questions with respect to requirements for the center highmounted stop lamp. 'l. Is it allowed to use 6 wedge-base-bulbs (3cp) on one high mounted stop lamp?' Federal Motor Vehicle Safety Standard No. l08 does not prescribe the number of bulbs to be used in the center highmounted stop lamp. Although paragraph S5.1.1.27(e) (formerly S4.1.1.41(e)) states that 'the bulb' shall be replaceable without the use of special tools, the intent of this language is not to restrict the number of light sources in the center lamp, but to ensure that any and all light sources are readily replaceable. Therefore, it is acceptable in principle to use 6 bulbs. The sole limitation is that the maximum candlepower limitation of the lamp specified in Figure l0 must not be exceeded. '2. SAE J186 Nov.82 says that the effective projected luminous area shall not be less than 29 square centimeters. How would you measure the projected luminous area of a lamp with 6 bulbs?' It is acceptable to measure the area as if the lamp contained only a single bulb. Incidentally, the November l982 version of SAE Jl86 has not been incorporated by reference into Standard No. l08 as the requirement for center highmounted stoplamps. The correct reference is Jl86a, September l977 (which does not contain the 29 square centimeter specification, that specification is expressed as 4 1/2 square inches in paragraph S5.1.1.27(a)). '3. Must each bulb reach the required photometric values?' No. Photometrics are a measure of the light output at specified test points measured from outside the lamp. Therefore, it is the lamp that meets the photometric requirements, and not the light source or sources. '4. What will happen, if one bulb is defect?' The specification for the lamp applies at the time it is sold to a retail customer. Thus, all bulbs in a lamp must be functional at that time. If a manufacturer chooses to design a lamp to meet the photometric specification when one bulb is not functioning, that would provide an extra measure of safety that is not required by Standard No. 108. Obviously, an inoperative light source should be replaced at the owner's earliest convenience, and the requirement that the light source be replaceable without special tools is intended to add to the convenience of replacement. Sincerely, Stephen P. Wood Acting Chief Counsel";