Interpretation ID: 1982-1.27

TYPE: INTERPRETATION-NHTSA

DATE: 03/25/82

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: United Sidecar Association, Inc. -- H. A. Kendall

TITLE: FMVSS INTERPRETATION

TEXT:

H. A. Kendall, Ph.D. United Sidecar Association, Inc. 1621 Palomino Lane Kingwood, Texas 77339

This is in reply to your letter of February 20, 1982, with respect to pulsating headlamps.

You have interpreted my letter of February 9, 1982 as stating that "for daytime operation of a motorcycle headlight, the light may be permitted to pulsate or modulate from one level of brightness to another." On the contrary, I stated that "a lamp whose intensity varies from a higher output to a lower output...would be prohibited." However, I also said that, if complete deactivation occurs (i.e., from a higher output to no output), then that mode of operation is permissible.

With respect to your latest letter and the problems of headlighting in older motorcycles, there would be no need to have the smaller bulb illuminated, and the "definite on/off/on/off sequence" you mention is sufficient for compliance with Standard No. 108.

Sincerely,

Frank Berndt Chief Counsel

February 20, 1982

Dear Mr Berndt:

My interpretation of your response of February 9, 1982 is that, for daytime operation of a motorcycle headlight, the light may be permitted to pulsate or modulate from one level of brightness to another.

Many of the older motorcycles with only marginal charging systems simply cannot cope with continuous lights on operation without frequent battery charging, externally, or without operating the engine at a very high speed in lower gears to keep the battery charged. However, almost all of the earlier machines have a nonsealed beam headlight containing a minor running (or parking) light in addition to the main twin filament.

As far as NHTSA is concerned, it would appear that as long as the smaller bulb was left on at all times (to provide the lower light output) that the main beam could be operated at some fractionally lower duty cycle, say, about 25%, at say 1.5 to 4 Hz, and still comply with NHTSA's ruling. If this is so, then it would be possible to allow older motorcycles to operate with a relatively simple inexpensive mechanical device to reduce headlight daytime consumption instead of using the very expensive solid state circuitry now available.

The main headlight would have a definite on/off/on/off sequence, however, the small continuous light would prevent the lamp from being extinguished at any time.

Please advise a ruling on this type of device for motorcycle headlights for daytime operation only.

Sincerely,

H. A. Kendall, Ph.D.

HAK/lk