modulators and their lighting regulations.
The Federal Law authorizing modulators; California Law; other States...
How pulsing light affects humans.
((ALSO: see Part 6 of: http://bmwmotorcycletech.info/lamps.htm))
© Copyright, 2012, R. Fleischer
NOTE: There is controversy over the use of headlight modulators. Several different viewpoints/arguments. Some find modulators annoying (I believe that is usually, perhaps not always, folks seeing OTHER folks' modulators, not their own...?). Some are concerned about oncoming drivers FIXATING on one's modulating headlight and thereby, somehow, aiming for them, this seems to mostly come from the idea that a motorcyclist tends to ride to wherever they fixate on. Whether or not to install a headlight modulator on YOUR bike, is a personal choice, obviously. My comments in this article apply to the USA, as headlight modulators may not be legal in some other Country's.
There ARE reasons that motorcycles are specified, since 1978 in California, and specified in many other States at various dates, to automatically, upon ignition turn-on, to have their headlights ON, without having to separately turn the headlight(s) on. State law and Federal law are not necessarily the same thing, but typically, Federal law supersedes. There is also an argument about certain cars, such as late models, having constant-on headlights...the argument usually is something on the order of motorcyclists want themselves to have such lights, to differentiate between them and cars. That's a decent argument, to my way of thinking.
But, the bottom-line is that a lot of safety agencies, and studies, have proven that safety is enhanced for motorcyclists having modulated headlights (and bright clothing, and certain colors of helmets, etc)....as it attracts attention, particularly important to a motorcyclist, who wants, or should want, an oncoming driver to notice/recognize that the motorcycle IS there. This has been shown to reduce left-turn accidents, and, in general, most biking accidents. I have been conducting experiments with reflective stripes on my sidecar rig, and have put an article on this subject on this website.
Thus, California had a law, early-on, about allowing modulators; and, NOW, all States must conform to the Federal Law allowing modulators. I suppose an argument could be made that such 'allowing' applies to only roads that had Federal money paying for all or some of those roads, but I have not dug into that, it being, in my opinion, rather a moot point. The major point is that a properly installed and operating modulated headlight is legally allowed, everyplace, in the USA.
It is also true, that no manufacturer supplies modulating headlights as standard, a relatively moot point, since the manufacturer would want the rider/owner to have the choice. I think it is possible that if a new major safety study comes about (I think it may be underway NOW), if modulators are tabulated for accidents, and are shown as beneficial, that we MIGHT end up with a Federal Rule/Regulation/Law, that all new motorcycles must have modulating headlights (probably meeting the specifications shown later in the article you are reading.
Note also that studies have shown that adding lights at the rear (and in some instances the sides) of motorcycles makes them more visible (and earlier recognized!). For the rear, the lights should be red, and as differentiated as possible between running and braking. Bright clothing, greenish-yellowish helmets, etc....all reduce accidents. I see no one arguing about 'fixating' on THEM.
The article, below, concerns itself with HEADLIGHTS, but a lot of the same science applies to lights in general.
The human eye
and brain; how light bursts and modulated light affects us:
It has been known for a very long time that human's eye/brain responses 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 seaside 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. NOTE that lighthouses had been in use for a very long time, long before there were electric powered lamps.
UNfortunately, Fresnel did NOT know about the Broca-Sulzer
Broca and Sulzer determined that short pulses of light of a CERTAIN DURATION will appear BRIGHTER than if the pulses lasted longer in time (or, for that matter, continuously!). There is much more to Broca-Sulzer, but here is what is important, on a practical basis, assuming a quite modest or brighter light source:
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. BUT...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. Also, if you think about it, and the above paragraph, the statement seems reversed....that is, the 0.150 second duration is only marginally brighter-appearing, than a SHORTER duration effect, comparatively.
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 want 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 humans (besides resetting our Circadian clocks, particularly BLUE light, etc.).
If the light is in continuous pulses of a certain width (time) and within a certain narrow range of pulse RATES, it will 'attract' even more attention by the human brain. Some ascribe this sensitivity to such as the brain's alpha rhythms....but this is only one explanation of several. There are some very scholarly articles regarding our ancestors and danger, and how the brain and eyesight and hearing evolved, etc. Won't get into it.
The Federal Law that
allows headlight modulators on motorcycles is a mixture of mostly
science, and some practicality....in that INCANDESCENT headlight
lamps (this includes Halogen's like the H4) can NOT physically 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 reasonably good one.
For a fuller explanation, yet not complicated to understand, read
the Federal Law, below.
HID: HID headlights are already fairly common. They don't turn on and off instantaneously. They are efficient, however, and if properly focused and shaped, the beams can be very good for bikers. UNfortunately, the simple bulb change KITS on the market are compromises. HID lights are much more difficult to modulate, due to arc re-establishment, and my guess is that we won't see HID headlights being modulated on motorcycles without some new developments.
LED: By mid-2012 we were already seeing some cars with LED headlights appearing in the highest priced cars. LED lights can be turned on and off just about instantaneously. Thus, an LED modulated headlight, with a PROPERLY DESIGNED modulator (and reflector and lens) might well be PERFECT for bikers. I have experimented with some modulators, and LED lamps, and find that all the modulators worked wonderfully with the LED lamps, better than Halogen H4 types!
The way the Federal Law
is written, I believe that modulated LED headlights will
comply with the Law, as written, IF they comply with this: "The lowest intensity at any test point shall be not less than 17
of the maximum intensity measured at the same point". On a practical basis it matters little, if that is complied with
...or not. The headlight could be fully turned off for its lowest intensity, as a practicality.
What will happen is that the LED modulators will be built to do this...or, the law will be changed...or both, or the modulators that do not comply will simply get away with not complying, as no one will much care. Section (f) will be, perhaps, changed, or, assumed to mean that it is only for incandescent lamps.
preliminary tests have been done on this effect, using various
'colors' of LED light. They show an increased recognition
Side note: Since 1979, most...but not all motorcycles sold... have had a 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
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
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
CHAPTER V--NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION, DEPARTMENT OF
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
S7.9.4 Motorcycle headlamp modulation system.
S18.104.22.168 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,
(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
(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.
S22.214.171.124(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 S126.96.36.199 (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
(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.
Here is an easy to read page on NHTSA use of modulators,
>>>>>Note that NHTSA says that the federal law overrides any State law.
(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.
Laws for various states for most everything
concerned with motorcycles:
Link is for Calfornia, but you can select any State:
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
road in the State, that has had Federal money involved, 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 specifies headlight on is section 25650.5, and the section 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 in that section.
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
10/02/2012: Add QR code; add language button; update Google Ad-Sense code
2013: remove language button as its scripting code had problems with some browsers.
09/15/2014: Clean up for clarity.
01/29/2015: Rechecked. Add a bit on conspicuity, etc...clarifying some statements. a tad more in Sept. 2015.
© Copyright, 2012, R. Fleischer
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