Informer: Motorcyclists may use modulators with lights

By 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