Interpretation ID: aiam2173
Commander
Enforcement Services Division
Department of California Highway Patrol
P.O. Box 898
Sacramento
CA
95804;
Dear Mr. Heath: This is in response to your letter of December 8, 1975, asking fou questions, the answers to which would provide an interpretation of Standard No. 108 with respect to separation distance of a turn signal lamp from the nearest edge of a Type 2 headlamp.; SAE Standard J588d, *Turn Signal Lamps*, June 1966, incorporated b reference in Standard No. 108, requires in pertinent part that 'The optical axis (filament center) of the front turn signal lamp shall be at least 4 inches from the inside diameter of the retaining ring of the headlamp unit providing the lower beam . . . .' We agree with your opinion that the reference to filament center may have been added because of the difficulty of determining the location of the optical axis in certain instances. In the vast majority of cases, however the filament center is on the optical axis, and the addition of the provision assists in determining compliance with the requirement.; You have asked:>>> '1. Is the filament center always to be taken as the center of th optical axis?'<<<; The answer to this question is no. In some instances the filamen center will not be on the optical axis. When this is the case the standard is ambiguous as to whether distance is measured from the optical axis or the filament center. While we prefer the optical axis, under the present wording either must be viewed as legally supportable.>>>; '2. Is the center of the emitted light always to be taken as the cente of the optical axis?'<<<; The answer is yes.>>> '3. If the answers to the above two questions are no, does the vehicl manufacturer have the choice as to which method is most favorable to him?'<<<; Yes, because of the ambiguity the manufacturer may choose either th optical axis or filament center as the point of measurement.>>>; '4. What is the optical axis of a two- or three- compartment lamp?'<<< The optical axis of a multi-compartment lamp is the center of the ligh emitted by the array, treated as a single complex light source. The 'half-value' method you described in your letter is a valid method of finding the optical axis of a complex light source as well as that of a simple one.; Finally you have asked whether, if we agree with the need fo clarification, the letter can be considered a petition for rulemaking or whether a formal petition should be submitted.; We agree that clarification is needed and accordingly plan to issue notice of proposed rulemaking in the near future.; Yours truly, Richard B. Dyson, Assistant Chief Counsel