Motorcycle Headlight Modulator Is A Bright Idea

Motorcyclists are paranoid about being hit by cars, and with reason. You’re a lot safer when you’re encased in a metal shell, with airbags and seatbelts. The mass difference between a car and a motorcycle doesn’t work out well for the biker, either. Unfortunately for bikers, motorcycles are also slimmer and generally less visible than cars.

A few decades ago, motorcycle manufacturers switched over to daytime running headlights to make bikes more visible. In the meantime, however, cars have done the same, leading many bikers to fear that their visibility advantage is losing it’s impact. The solution? Blink the headlights gently during the daytime, and run them normally at night.

[William Dudley] was unsatisfied with commercial versions, so he built a custom headlight modulator for his motorcycle.

head_mod_cds_7_schem And believe it or not, he did it with a 555 timer IC and a light-dependent resistor (plus some transistors and a whole slew of miscellaneous parts). But [William]’s design is a good one, and he walks you through all of the choices he made in building the light-sensing circuit that disables the 555.

Whether you need a motorcycle headlight modulator or are interested to learn how this problem would be solved in the pre-Arduino days, go check out [William]’s post. And while you’re on the nostalgic electronics trip, check out this nixie tube speedometer.

52 thoughts on “Motorcycle Headlight Modulator Is A Bright Idea

    1. > Are you sure this project belongs on HaD? /s

      15 years ago in a galaxy far far away someone would have suggested a beowulf cluster of 555s, only to get as a reply a link to a 556 data sheet.

    1. Just read the bit on legality on his website, what good does a modulater do in terms of visibility if the modulation happens at 3 to 5 cycles per second with 50 to 70% of the cycle at max intensity? Thats just annoying, not really attention grabbing. (It also makes judging speed and relative position more difficult usually)

      I’m not a biker, but I don’t really see the advantage here.

      1. I ride and ride a lot. Every dry day, light rain and all Winter long. I’ve always like to say “You’re never too old and it’s never too cold for a bad idea”

        According to a government study called the Hurt Report the predominating cause of motorcycle fatalities is not being seen. You’ll hear every biker say things to the effect of, “ride like you’re invisible, that no one can see you and every car is going to pull out in front of you or side swipe you”. Which is good advice!

        I’ve read a bit about the psychology/biology of why people think headlight modulators work. Since a lot of this is psychology it’ll be a bit hard to swallow just how factual this all could be, but food for thought anyway.

        Some state that while we’re driving a car in a place like the USA where there are way more cars to motorcycles, our brains get trained to expect to see something that looks like a car. Brain will expect to see two headlights, overall shape of a car, overall size of a car. With your first glance your eyes don’t even see the motorcycle cause it doesn’t fit the brain’s assumption of what it expects to see. I personally believe this may be true, Ive ridden motorcycles for many years with hundreds of thousands of miles and I’m guilty myself of not seeing another motorcyclist when pulling out or changing lanes. Had some close calls! We can be hard to spot so look twice!

        Then others get into the biology side of things where human’s are pay more attention to things that stick out, motion, flashing lights, bright colors, loud patterns. One I found kinda interesting was about adding two lights down lower on your forks. Something to do about having a triangle of lights triggers our more primal side where we see a face or more specifically a face’s “eyes” and more likely to subconsciously recognize an object. Even adding big eyeball stickers on a windscreen is said to be helpful.

        I’ve got a modulator on my current bike and tho it’s matter of my lowly opinion; I do think it helps. I’ve noticed a few others riders in town with em and I certainly noticed them quicker with a modulator than without. Specifically one time when the sun was low on the horizon riding straight into the sun, creating bad visibility. A pair of guys riding towards me, one had a modulator and one did not. I spotted the guy with the modulator immediately but the guy without one I couldn’t see till he was within around 40 yards of me.

        Modulators? May not be 100% effective, hell may even just be placebo, but in the right circumstances it could mean the difference between a good time and a bad time on the road.

        1. The problem with that theory is that our brains seek out novelty. If we’re trained to see two headlights, car shape, etc, when something breaks the pattern our attention gets focused on it. We don’t glance over the unexpected; that’s a great way to get eaten by a tiger! If anything, that’s why modulation works. A blinking light is weird and out of the ordinary, it gets attention.

        2. No, don’t ride as if you are invisible. You need ride to as if every car driver actually wants to kill you. Assume that every car is being driven by a crazed nutjob that hates bikers and wants you dead.

          Always have an escape route, practice emergency stops and avoidance maneuvers every single spring and every fall. I spend 3 hours in a local parking lot with some chalk drawing up hazards (wife bought me some traffic cones this year) and practice avoidance and panic stops over and over again. Learn how to use that front brake well.

          Sadly a lot of riders don’t really know how to ride and rarely use the front brake where 70% of the bikes stopping power is.

    2. I Sweden it’s illegal to have any blinking lights forward. Strictly speaking, this could be interpreted as “you are not allowed to PWM your lights at all”, no one’s gonna notice. Backwards it’s allowed, as long as the frequency is above 200/minute (about 3Hz).
      Personally, I thinks it’s really annoying and might actually be dangerous if the frquency is very low. Say the frequency is 1Hz. A car will travel a long distance in 1 second…
      Just get a fucking reflex vest! They cost like 5 bucks. And keep your lights steady on.

      1. The blinking lights are not allowed because people confuse them with the police, emergency vehicles, or other unusual things and start peeking at their rear-view mirror and driving erratically.

        If someone’s blinking you with their headlights, it usually means something like, you forgot your groceries on the roof of the car and they want you to stop etc. and that causes accidents because your attention is consumed by trying to figure out what the hell’s going on.

        1. You guys need to learn what a modulator does.
          It does not ‘blink’ the lights on and off, it simply varies the brightness of the light.
          It’s not a strobe, it’s not a flash.

          You ever notice when oncoming traffic or an old motorcycle is heading toward you, it almost looks like they are on a bumpy road and the light kind of flickers? That’s what this does.

          1. Unfortunately the circuit described in the article doesn’t do that. It drives the headlight on/off, and there’s no description in the original article as to how it achieves the legal requirements in practice.

            You could connect it to the high beams, but then you’d be flashing people with the high beams all the time.

          2. Everyone here should stop being Lazy and if they have the urge to make negative comments they should first avail themselves of what is modulation as related to motorcycle headlights. Here is link that contains other links to the legality to the reasoning and a short video showing you just what this really is. After all of that then you have the right to leave either a thought or else something scientific to support your negative position.. link:

  1. I see a problem when the sensor is lit by a passing car. Then your light starts pulsating and you’ll see nothing/not much, which can get rather unpleasant or even dangerous. Or am I wrong?

    1. Basically, you have 2 x 55 Watt H4 bulbs which produce about 20 lumens per Watt or roughly 2200 lumens. A lux is a lumen per square meter, so projecting the car headlights on a surface about the size of a large garage door would give you something like 100 lux. A brightly lit room is about 100 lux.

      As a rule of thumb, a rainy day is 1000 lux, and a bright day is 10,000 lux, and direct sunlight is 100,000 lux so there’s at least an order of magnitude difference in brightness between a car headlight pointing at you, and daylight.

  2. You could modulate the headlights at a specific frequency A sensor in cars could pick up on the modulation and prompt the driver with a warning (like a fasten seatbelt beep) when the modulated light is seen.

    It could encode bike speed in the modulation. Encoding the speed allows for not warning if the bike is following the car for a period of time (same speed.)

  3. The Hurt report is quite an old piece of research, if I recall correctly it was written by a car driver who pulled out on a motorcycle, and went on to research how he failed to notice the approach of the motorcycle.
    He also went further into the whole subject of motorcycle / car collisions, I also remember seeing graphics detailing the relative hard and soft points on the body of a car.
    As many have already pointed out most countries have legislation that prohibits pulsing / flashing lights on the front of motorcycles.
    However it is interesting to note that an overwhelming majority of cyclists seem to fit pulsing / flashing on the front of their bikes in the interests of safety, and despite the widespread use I have not seen any “crackdowns” to stop it.
    Perhaps there is some mileage in using LED lights intended for a bicycle as supplementary lighting on a motorcycle.

    1. The bicyclist aren’t much of an issue because the blinking LED lights are little 3xAAA battery powered twinkles that pulse relatively rapidly, so you don’t get the same effect as proper full-power headlights flashing in the dark.

      They’re usually completely overpowered by street lighting, as in, if you point the torch a couple meters ahead of you on the ground, you can’t tell if it’s on or off. As such they don’t draw that much attention.

      Of course there’s the people who strap HID lights and 30W LED modules to their bikes, but they’re sensible enough not to go blinking them on public roads.

      1. They do to a certain extent here (college town) but from experience the gigawatt strobe blinkies on a dark road will give even a non-epileptic a seizure and people give up on that pretty quickly. I use a good bright light forward with a smaller blinker so that doesn’t happen – effectively modulation -and it’s very visible.

        As an aside, complete on-off modulation can be very hard to get a distance/position fix on while driving a car so partial modulation is a great idea forward and backward. I see bikes with flashing-only taillights and it seems to increase the usual autokinetic effects (the flashing light seems to be in different positions due to eye movement).

        The laser line markers seem like a great idea but the real hazard seems to be people who value their social life more than your mortal existence, driving while texting, and they don’t see it because they’re not even looking.

  4. For those who don’t read the whole article, or are not familiar with motorcycles. Federal law (U.S.) allows, and as I interpret it, encourages these as a way to make motorcycles more visible during the day. Most states that I am familiar with REQUIRE a motorcycle to run headlights during day light hours to increase visibility. Modulators are not *required* however.
    The ‘Hacker’ in question rigged a light sensor for daylight. It is NOT pointed at oncoming traffic to activate because of a passing car. The way he has set it up is so that it will NOT activate after daylight hours. During the day, the pulsing light is certainly attention grabbing, but not overly distracting. I have seen them many times in oncoming traffic while I was driving my non-motorcycle vehicle. (A.k.a. “The Cage”)
    There are several versions of this that I have seen that are either manually triggered, or much as this fellow here did, light sensitive (day versus night. They have cars that do the same for headlights. My grandfather had one.) My motorcycle doesn’t currently have one, but I’m considering adding one, as well as a pulsating brake light.
    Motorcyclists are often encouraged to “ride like they’re invisible” Because the first thing you hear after getting hit, is the other driver saying “I didn’t see him/her!” Many people slip into an ‘autopilot’ mode while driving, and because there are not as many motorcycles out there as cars, they don’t expect to see them, and therefore, *don’t*. Small things like these seem to help.
    I’m a motorcyclist, and I make a conscious effort to look for motorcycles, and sure enough, I miss them sometimes too. There is nothing wrong with this from a safety stand point, aside from the danger you risk of riding at night if it some how fails completely and your head light goes out.

    1. “Most states that I am familiar with REQUIRE a motorcycle to run headlights during day light hours to increase visibility.”
      In Australia, motorbikes are required to have their headlights hard-wired on. Bikes here don’t have light on/off switches, they just have a high/low beam rocker switch.

      As for the ‘ride like your invisible’ thing, it’s spot on. Assume nothing and expect every car to pull out on you, change lanes on you etc. Plan your evasive action in advance as you approach any side road with a car in it. Also, stay close behind/between other cars while near intersections to use their bulk to shield yourself (it’s funny how people see a car heavy enough to kill them, but can’t see a bike in the same place even if it’s lit up like a Christmas tree.)

    2. It’s not state laws but rather federal regulations that require headlamps lit up on motorcycles. In the US and Canada, FMVSS108 & CMVSS108, respectively, require the headlamp on a motorcycle manufactured after some date in the early 1970’s, the exact date escapes me at the moment, to be illuminated when the engine is running. There is also wording in those regulations specifically addressing the modulated headlamp.

  5. Im glad we have strict traffic laws here in Spain, Im a biker too but I don’t like the idea of people having so much fredom designing “what’s good” and “what is not” to be sharing the road with others. Here you can’t just have that. Everything is stated and a headlight can’t be flashing, blinkers have to be strictly orange and at a certain frequency, stop light can’t flash either, and so on…
    Yes it can be very distracting.

  6. Actually recent studies show that adding a pair of 10Watt yellow LED driving lights to the motorcycle it gets the attention of drivers far more than the modulating headlight as very bright yellow lights in a triangle with a headlight draws their attention.

    The AMA actually discourages riders from using headlight modulators as they also significantly reduce lamp life, and nothing sucks more than changing your headlamp at night on the side of the road….. that’s if you are smart enough to carry a spare bulb, I know a lot of riders that don’t even carry a tool kit.

    1. Modulated headlights lead to target fixation.

      I’ve found myself doing this with bikes that have modulators… I lock onto them, and the car/bike goes where I look… you end up veering towards the biker with the modulator rather than away.

      I won’t put a headlight modulator on my bike for that reason, though I do think that a brake light modulator (While questionably legal in my state) is handy, I just end up pumping the brakes when I stop and blinking them manually when some one is coming up behind me to fast (or more that I feel they are coming in to fast).
      Perfectly legal, but requires a bit more attention to be paid, which is best when you are on a bike, the murderous cagers around you require your full attention.

    2. Reducing lamp life using a modulator is absolutely not true…life is actually extended and in halogen lights it helps to prevent crystallization which shortens the bulb life.

  7. I’ve seen this comment more than once,
    Do some research before you post or assume to know how something operates.

    A motorcycle headlight modulator does not ‘Flash’ or ‘Blink’ the front headlight. It varies the brightness, but the headlight will be on 100% of the time. It has a similar effect of what a car or motorcycle might look like to oncoming traffic if it was travelling on a a bumpy/gravel road. You know what else causes this behaviour? Your local kids that put huge amps and subs in their vehicle without proper wiring or a big enough alternator. Their lights dim too.

      1. I believe that the “headlight never goes black” requirement is met by the decay of the tungsten filament. Even though the current goes to zero, the filament remains hot enough to emit light. I have not verified this experimentally, but I compared my modulator to a commercial one (the Kisan linked to in the article) and the Kisan also shuts the current off entirely. If the duty cycle is moved toward 70% this effect should be even stronger (as there is less time for the filament to cool). This is also why the filament isn’t stressed as much as one would think, because it never cools down.

  8. What’s it like for the biker with one of these modulators? I’ve never used one (in fact, I’m not a biker), but it seems like it would be fatiguing or cause headaches after some time to have a subtle (or maybe not-so subtle) flicker on everything you see.

    1. They’re daytime use only, you’ll notice it reflecting on cars in front of you at a light or off reflective road signs but it’s really a mild effect. Doesn’t bother me, but does remind me that the headlight is still working which is some piece of mind.

    1. I don’t think this scheme will work if the modulator has a photocell function, because once it gets dark, the headlight would be full-on and the cap would never charge, leading to the headlight switching off, leading to oscillation that depends on the discharge rate of the big electrolytic. So this scheme works only if you have a manual switch to turn off the modulation after dark. Correct me if I’m wrong . . .

      1. @ William F. Dudley Jr.:

        You’ve got it! The modulator works as long as there is enough daylight to counterbalance the varying light. They are only intended to be used in hours of daylight.

        @ Dax:

        Think of the effect as POV. Electrically the filament, or LEDs, are turned off but visually the effect is like sunlight shining on a lake with small waves. The light appears constant but visually ‘warbles’.

        There is a variant where the headlight high beam is kept on and the low beam is modulated.

        O live in the country where the world’s most skilled, bad drivers live – VietNam – and I have upgraded my headlights to PWM based on LadyAda’s Bedazzler. I can run normally, have a modulated headlight and for Open Tour buses I use the Dazzler. It works a charm.

  9. This is an interesting problem we face.

    Unfortunately (or fortunately, however you look at it), our police vehicles in Australia have 2 large spotlights fitted to the bumper that blink brightly in sequence – accompanying the red and blue lights when trying to get through traffic in an emergency.

    So even if say this were to be legal, (or not illegal), it would inadvertently mitigate the effects of emergency vehicles the same way car drivers did to motorcycles with the daytime running lights.

    When i swapped my halogen w/reflectors to a HID lamp w/projectors, i used 55W bulbs shining brightly at 4300k. While this isn’t exactly legal in my country, i tried to find the balance between stupidly illegal (i.e. 7000k blue lights with no cutoff), and safe for me.
    Originally, the bike was manufactured to have 1 halogen on at all times, with the high beam “second bulb” switched by the rider.
    What i ended up with was 2 HID 55W globes cut off at a point that wouldn’t blind oncoming traffic. I also modified the wiring slightly so that i could have both low or both high at any given time.
    When i would ride in the day, i would have both on high beams.

    Once when i was riding about 500m to 1km behind my mate’s car, he told me once we stopped that i was more visible than the cars next to me, in broad daylight.

    I was never able to test this properly and take photos, although HIDs (or leds – whichever you prefer) seem to work really well for the time being.

    I don’t think the battle for presence on the road should be approached visually any more as we are losing visual space through a million other distractions, but maybe we should also look at other mediums, i.e. sound navigation/ranging, radio detection, etc

    1. Blue lights in the dark are counterproductive.

      It’s because we have a fourth visual pigment in the eye that’s responsible for night vision, and when the light levels go sufficiently low it becomes active and starts to amplify the eye’s response to blue light. That however means the other colors become darker (Purkinje’s effect). Moonlight for example is the same color temperature as sunlight – the moon is simply reflecting the sun – it’s just low intensity so we percieve it as blue.

      Under low light conditions, if you have a blue light source, it makes the eye respond as if it was recieiving more light than it actually is getting – the pupil contracts slightly – and that further amplifies the loss of other colors and makes anything outside your beam that much harder to see.

      1. We’ve basically evolved in an environment where the ambient color temperature turns from green-blue to yellow-red as the light levels fall, and then back to green-blue when the sun is below the horizon, so our eyes adjust their color response by amplifying blue, and then finally dropping color vision off completely.

        The problem for drivers is that night vision has really low resolution. It’s so bad you can’t read a road sign 25 yards away because the fovea, center of the visual field, is disabled. In order to see things, you have to look slightly to the side because you go blind in the middle.

        In order to see well enough to drive in the dark, we need enough light for color vision so the fovea becomes active, but that means we’re operating in a mode that expects a color temperature that is heavily in the red end of the spectrum.

        You’d think that using blue lights in the dark would allow you to see more with less light, because the eye is extra-sensitive to it, but the eye adjusts its light response based on the expectation that the spectrum is shifting towards blue as the light levels increase, so upon seeing blue light it simply assumes there’s more light than there actually is and you become blinded.

        It’s one of those stupid shortcuts of evolution, like how breathing isn’t based on the amount of oxygen in your blood, but on the amount of carbon dioxide, on the assumption that if you breathe enough to keep the CO2 levels low you automatically get enough O2 to survive. In fact, even if you hold your breath till you’re about to burst, you rarely go below 85% oxygen saturation. Trouble is, if for some reason there isn’t enough O2 around to keep you topped up, you won’t notice it and you die.

        1. This is really interesting. Most people aren’t aware to the implications blue light has under low light conditions. Neither was i aware until i read your post.

          It explains the times I’ve been almost completely visually impaired by a police car pulled over on the side of the road, despite there being plenty of other light sources.

          My reasoning for the 4300k light is that it has been generally accepted to be the colour temperature region with the highest output of light.
          This was chosen less because of night vision, but more because of a necessity to stand out from the road glare from our harsh, Western Australian sun. Our relatively low atmospheric nitrogen dioxide concentration, coupled with low humidity and pollution creates an ideal condition for a more “true” sunlight, similar to that of the more remote parts of the world.

          However, given your comment, it further iterates itself as a temperature of light that finds a balance between light output and impairment of colour vision, probably the most ideal to our biology under low light conditions.

          1. The human eye has a hard time focusing on blue and shorter wave lengths (violet). Especially when the intensity of the light is far higher than background light levels.

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