Interpretation ID: nht93-7.4

DATE: October 1, 1993 (EST)

FROM: John Womack -- Acting Chief Counsel, NHTSA

TO: Richard Horian -- President, Woodleaf Corporation

TITLE: None

ATTACHMT: Attached to letter (fax) dated 8/12/93 from Richard Horian to Michael Perel (OCC 9016)

TEXT:

This is in response to your FAX of August 12, 1993, to Michael Perel of this agency regarding your "sudden brake indicator hazard light."

You were informed on December 7, 1992, by Paul Jackson Rice, then the Chief Counsel, that this auxiliary item of lighting equipment would be permissible as original equipment since it did not appear that it would impair the effectiveness of any of the lighting equipment required by Standard No. 108. You now ask "(w)hat is the fastest flash rate or range of flash rates expressed in 'flashes per minute' that are allowed by Federal law."

Standard No. 108 does not specify any range of flash rates for items of supplementary lighting equipment, thus, the choice is that of the manufacturer. The standard does specify a flash rate for turn sign and hazard warning signal lamps which are required by the standard. The flash rate for these lamps is 60 to 120 flashes per minute. In addition, S5.6 of the standard specifies a motorcycle headlamp modulation rate of 240 cycles per minute, plus or minus 40 cycles per minute.

The cycling and modulation rates of lighting systems are very important to motor vehicle safety because of a phenomenon known as "photic driving." This issue concerns potential adverse reactions in some people similar to epileptic seizures. The condition is brought on by certain regularly flashing lights, even in some persons not otherwise susceptible to epilepsy. From available studies, it appears that people are most likely to be affected if the flash rate is about ten flashes per second (600 flashes per minute) and/or when the background is very dark.