Interpretation ID: nht68-3.44

DATE: 07/26/68

FROM: AUTHOR UNAVAILABLE; David A. Fay; NHTSA

TO: Toyota Motor Company

TITLE: FMVSS INTERPRETATION

TEXT: Thank you for your letter of June 27, 1968, in which you requested clarification of the term "optically combined" as applied to motor vehicle lights.

"Optically combined" in this context means that the same lens area is used for more than one function such as tail and stop lights or stop and turn signal lights or tail, stop and turn signal lights. The normal means used to accomplish this "optically combined" lamp has been to incorporate a single dual-filament bulb with a reflector and lens.

Since the design of your Toyota Crown combination stop, tail and turn signal lamp is such that a different part of the lamp area is used for the turn signal lamp, we do not interpret it to be optically combined with the tail and stop lamp.

The concurrence of the above interpretation with yours and that of the California Highway Patrol should not be construed to be an approval of your design. The results of recent research on lighting and signaling reviewed by this Bureau indicate that signal lights should be separated 4 1/2 to 5 inches minimum (centerline to centerline separation.) Although no dimensions are specified on your drawing it appears to be approximately full scale with a separation distance of 2 1/2 inches between the stop and turn signal lamps. The steady-burning stop lamp may therefore "wash out" or significantly reduce the effectiveness on the turn signal lamp. Federal Motor Vehicle Safety Standard No. 108 does not require a minimum separation distance between signal lights; however, upon completion of our present research contracts on rear lighting and signaling, we may consider such a requirement in the future.