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Informer: Motorcyclists may use modulators with lights

Last Modified: Monday, November 18, 2013 11:52 AM

By Andrew Perzo / American Press

Is it legal for motorcycles to have head lamps that flash?


State law says that “flashing lights are prohibited except on authorized emergency vehicles, school buses, or on any vehicle as a means of indicating a right or left turn, or the presence of a vehicular traffic hazard requiring unusual care in approaching, overtaking or passing.”

But federal vehicle standards, which supersede state law, permit motorcyclists to outfit their bikes with head lamp modulators — the wiring setups responsible for the flashing headlights.

Federal regulations — 49 CFR 571.108 — say that “a headlamp on a motorcycle may be wired to modulate either the upper beam or the lower beam from its maximum intensity to a lesser intensity.” But the system must meet certain standards.

Among them:

“The rate of modulation shall be 240 ±40 cycles per minute.”

“The headlamp shall be operated at maximum power for 50 to 70 percent of each cycle.”

“The lowest intensity at any test point shall be not less than 17 percent of the maximum intensity measured at the same point.”

“The modulator switch shall be wired in the power lead of the beam filament being modulated and not in the ground side of the circuit.”

“Means shall be provided so that both the lower beam and upper beam remain operable in the event of a modulator failure.”

‘Safety margins’

According to a National Highway Traffic Safety Administration report released in November 2011, a modulated high-beam head lamp on motorcycles was one of three alternative lighting methods that reduced the likelihood that automobile drivers would turn in front of motorcyclists.

Researchers tracked the gaze of 32 study participants who sat in a parked, median-situated vehicle and were asked to judge when it was safe to turn left in front of oncoming traffic.

“The participant’s eye movements were recorded by a head-mounted eye tracking device. This allowed researchers to evaluate the effects of motorcycle lighting treatments on the frequency, timing, and duration of gaze fixations on the approaching motorcycle,” reads the report.

“The primary dependent variable was the time between the participant’s indication that it was no longer safe to initiate a turn maneuver in front of the approaching motorcycle and the arrival time of the motorcycle. This time difference was called the ‘safety margin’ for the purposes of this study.”

According to the report, low-mounted auxiliary lamps, the modulated high-beam head lamp and a four-lamp auxiliary array “were most effective at reducing short safety margins.”


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The Informer answers questions from readers each Sunday, Monday and Wednesday. It is researched and written by Andrew Perzo, an American Press staff writer. To ask a question, call 494-4098, press 5 and leave voice mail, or email

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