Federal law allows for "modulating" white lights on the front of motorcycles for safety. Some companies have pushed this a bit with the flashing LEDs. I have some that were marketed as "modulating", but they definitely flash, so I haven't mounted them. I want to hear from a Judge that they would be allowed first.---------------------------.
Modulation is allowed for HEADLIGHTS (either low or high beam, not both. Modulation is strictly defined in the federal documents, and cannot FLASH on and off. They can only be modulated from full on to a reduced level, never full off. The modulation rate is also specified, and must be withing certain limits.
Those flashing lights on your friend's bike are absolutely illegal, and could net him a big ticket!
Here is the section of the federal regulations regarding motorcycle headlight modulation:
S7.9.4 Motorcycle headlamp modulation system.
S188.8.131.52 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, provided that:
(a) The rate of modulation shall be 240 <plus-minus> 40 cycles per
(b) The headlamp shall be operated at maximum power for 50 to 70
percent of each cycle.
(c) The lowest intensity at any test point shall be not less than 17
percent of the maximum intensity measured at the same point.
(d) 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.
(e) Means shall be provided so that both the lower beam and upper
beam remain operable in the event of a modulator failure.
(f) The system shall include a sensor mounted with the axis of its
sensing element perpendicular to a horizontal plane. Headlamp modulation
shall cease whenever the level of light emitted by a tungsten filament
light operating at 3000 deg. Kelvin is either less than 270 lux (25
foot-candles) of direct light for upward pointing sensors or less than
60 lux (5.6 foot-candles) of reflected light for downward pointing
sensors. The light is measured by a silicon cell type light meter that
is located at the sensor and pointing in the same direction as the
sensor. A Kodak Gray Card (Kodak R-27) is placed at ground level to
simulate the road surface in testing downward pointing sensors.
(g) When tested in accordance with the test profile shown in Figure
9, the voltage drop across the modulator when the lamp is on at all test
conditions for 12 volt systems and 6 volt systems shall not be greater
than .45 volt.
The modulator shall meet all the provisions of the standard after
completion of the test profile shown in Figure 9.
(h) Means shall be provided so that both the lower and upper beam
function at design voltage when the headlamp control switch is in either
the lower or upper beam position when the modulator is off.
S184.108.40.206(a) Each motorcycle headlamp modulator not intended as
original equipment, or its container, shall be labeled with the maximum
wattage, and the minimum wattage appropriate for its use. Additionally,
each such modulator shall comply with S220.127.116.11 (a) through (g) when
connected to a headlamp of the maximum rated power and a headlamp of the
minimum rated power, and shall provide means so that the modulated beam
functions at design voltage when the modulator is off.
(b) Instructions, with a diagram, shall be provided for mounting the
light sensor including location on the motorcycle, distance above the
road surface, and orientation with respect to the light.