Headlight modulator law and regulations

Headlight modulators and complete lighting regulations.
The Federal Law authorizing modulators; and, California Law; and other States...

© Copyright, 2011, R. Fleischer

The human eye and brain; how light bursts and modulated light affects us:
We humans have some characteristics that are common with other primates. Some of our responses, particularly to color and light bursts, are relatively unique.

Simplified, here are some things you might like to know.   Since you likely already 'know' that a headlight modulator causes 'attention-grabbing' by other humans, and I WANT you to READ this...I will put the section on bursts, first:

It has been known for a very long time that our eye/brain response to light bursts are peculiar. Some of today's knowledge about this subject was known by such as Augustin Fresnel, who invented the Fresnel Lens (which, when rotated, was used in Lighthouses, up until perhaps the mid-20th century). Fresnel found that using a lot of prisms in such a position as to result in a collimated radial light beam, would produce a beam of light that could be seen by mariners at a great distance. UNfortunately, Fresnel did NOT know about the Broca-Sulzer Effect.   Broca and Sulzer determined that short pulses of light of a CERTAIN DURATION will appear BRIGHTER than if the pulses are longer in time (or, for that matter, continuous!).   They developed a chart.   The Broca-Sulzer Effect requires that the light intensity be at least 25 Lux to be relatively noticeable....and as the light intensity increases, the Broca-Sulzer effect becomes very pronounced. Further, as light intensity increases above 25 Lux, the peak effect is at more and more reduced light duration.
On a practical basis, here is what this all means:
If the light duration is over 0.150 second, the light burst only marginally appears brighter than a continuous light. The effect is more if the light is quite bright.
If the light duration is around 0.044 second, a light of maybe 150 to a few hundred Lux, will appear VERY much brighter than a continuous light.

Now, I will guess here that some of you will immediately say something like: "Well, bright light causes the eye's pupil to contract, to protect the eye, so a short burst will not last long enough for the pupil to change size". You'd be only partially correct.

Broca and Sulzer's work was published in 1902. Similar work was done by Blondel and Rey in 1911.

The bottom-line here is that if you wanted a light to attract attention, without having it monstrously bright, one method is to have the light come in short bursts, lasting on the order of 0.030 second to maybe 0.200 second. Thus, a headlight with a short burst of light, will be more visible to others, than one running continuously yet of considerably higher power. Think about that. On a practical basis, when you WANT your headlight to be visible by oncoming traffic, perhaps so they do not turn left in front of you, you can use a modulated headlight beam of the 'right' characteristics, and it will be MORE attention-getting than a rather substantially more powerful headlight.

This is NOT the only strange effect of light on us (besides resetting our Circadian clocks, etc.).
If the light is in continuous pulses and within a certain narrow range of pulse RATES, it will 'attract' even more attention from the human brain. Some ascribe this sensitivity to such as the brain's alpha rhythms....but this is only one explanation of several. The Federal Law that allows headlight modulators on motorcycles is a mixture of mostly science, and some practicality....in that INCANDESCENT headlight lamps can NOT have their ACTUAL LIGHT OUTPUT decrease to anywhere's near zero, at the modulating RATE that is best to attract attention by the human brain. This is due to the hot filament being unable to cool fast enough during the OFF period, and heat up fast enough for the ON period. Thus, the Federal requirements are a compromise, although a good one. For a fuller explanation, yet not complicated to understand, read the Federal Law, below.

I note here that HID headlights and likely also LED lights, will eventually be very common. I anticipate these will bring about their own special effects on us, as well as bringing some solvable problems. I also note here that in some near-future time, LED headlights will become common. Since LED's can be turned on (and off) for a very high percentage of final light output (they are nearly instantaneous), an LED modulated headlight might well be able to be PERFECT for attention getting by humans. The way the Federal Law is written, it appears TO ME, that modulated LED headlights will comply with the Law, as written, IF this is complied with, see (2) (c) below: The lowest intensity at any test point shall be not less than 17 percent of the maximum intensity measured at the same point.
What will happen is that the LED modulators will be built to do this...or, the law will be changed...or both. Section (f) will be changed, or, assumed to mean that it is only for incandescent lamps.

Some preliminary tests have been done on this effect, using various 'colors' of LED light. They show an increased recognition effect.

Since 1979, most...but not all....motorcycles sold have had headlight ON function when the ignition is on. This was done by most manufacturer's due to some States having laws that said that the headlight must be on.

To the best of my knowledge Federal Motor Vehicle Safety Standards do not 'require' daytime headlamps on motorcycles.
Reference: http://edocket.access.gpo.gov/cfr_2004/octqtr/49cfr571.108.htm This is the Federal Motor Vehicle Safety Standard 108, usually just shown as FMVSS 108.
Note: this long hard-to-read article has a chart section, well-buried, that is JUST for MOTORCYCLES. In this chart the Federal Government has SPECIFIED maximum brightness of your headlight, in Candelas.
I mention this, as many of you have installed over-size headlights. Of course, few are ever stopped for such.

NOTE that in Canada, there is also a similar document, but it is referred to as CMVSS 108, and it DOES require daytime lamps on bikes, from 1/1/90 (If I remember correctly).

Some States do require daytime running headlamps, and new production, from 1/1/90, at least was encouraged, Federally, therefore motorcycle manufacturers began equipping all motorcycles built for sale in the U.S. with them. (Here's another website describing current federal regulations, regarding motorcycle lighting, including headlamp modulating devices) http://calcoast-itl.com/assets/Motorcycles%20&%20Motor%20Driven%20Cycles%20-%20Lighting.pdf

WAIS Document Retrieval[Code of Federal Regulations]
[Title 49, Volume 5]
[Revised as of October 1, 2001]
From the U.S. Government Printing Office via GPO Access
[CITE: 49CFR571.108]
TITLE 49--TRANSPORTATION
CHAPTER V--NATIONAL HIGHWAY TRAFFIC
SAFETY ADMINISTRATION, DEPARTMENT
OF TRANSPORTATION
PART 571--FEDERAL MOTOR VEHICLE SAFETY STANDARDS--Table of Contents
Subpart B--Federal Motor Vehicle Safety Standards
Sec. 571.108 Standard No. 108; Lamps, reflective devices, and associated
equipment.
S7.9.4 Motorcycle headlamp modulation system.
S7.9.4.1 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 minute.
(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.
S7.9.4.2(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 S7.9.4.1 (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.

(4) Article IV, section 2, of the U.S. Constitution is held to say that Federal Law is superior to and overrides State Law, when they conflict.

California law is very brief.   Federal Law will supersede California law on Federal Highways, and on highways/roads that were paid for in part or wholly by federal funds. I believe that Federal Law will supersede any State's Law, on a practical basis, if not an absolute basis, on any State road, that has had Federal money, or not.
Knowing the broad brush law in YOUR home State may be of some help, if ever a question on modulators. You can check YOUR State's laws, but I will bet that any Court will hold that the Federal law applies.
California Vehicle Code that allows motorcycles to have modulators is 25251.2.
It specifies that the UPPER beam is to be modulated (note that Federal law allows either). California Law provides only that the modulation is between a higher and a lower brightness, at a 200-280 rate, and not to be used in darkness.   This is basically like the federal law...except that California has NONE of the fancy specifications from (a) onwards, as in the federal law, in (2), above.

OFFICIAL California Vehicle Code definition of DARKNESS is in section 280 of the California Vehicle Code. Darkness is defined as 1/2 hour after sunset to 1/2 hour before sunrise; or at any other time visibility is not sufficient to clearly....discern....any person or vehicle on the highway (yes, they do say highway), at 1000 feet.   They do NOT specify what sunrise and sunset is, at least in that section.

Rev:
04/12/2010: Add California Vehicle Law information
05/22/2010: Add technical information on human eye sensitivity to light bursts and modulated light, and clean up article somewhat.
10/08/2010: Split the Federal Law section into 2, and add (1)
06/08/2011: Clean up article
06/25/2011: Clear up...somewhat!....Federal and California Law