Seizure-Inducing Bicycle Lights

Flashing Bicycle Light


Granted, the photo at the top of this post isn’t the finest representation of those blindingly blinking headlights which have become so common on bicycles today. But without hauling out semi-professional photographic gear, this was as close to capturing the pulsing light as I could come.

With each passing day, it seems, these lights become brighter. New technologies allow greater output in increasingly smaller casings. And, the flash patterns vary. Some lights offer more than one pattern. Others offer only a single pattern, but it’s an off-beat sort of pattern, that is not only attention-getting, but highly annoying.

But, perhaps that’s the point. An annoying light is difficult to miss. And, if the light isn’t missed, neither is the bicycle. Or so the theory goes.

There are pros and cons to such lights. Under certain conditions, where a bicycle might be difficult to see, they draw a driver’s attention to the spot where the cyclist is riding. Examples of times where this might be beneficial are in heavy traffic, when a driver’s attention is divided in multiple directions and on dark roads where a driver might not expect to see a bicycle.

At times like these, flashing white lights might mean the difference between a car noticing a bicycle and avoiding it and a car not noticing anything in its path and striking a bicycle. So, there is a definite safety advantage in situations where a bicycle might not be otherwise seen.

But, what about cases when people ride on moderately trafficked suburban roads with decent lighting, less congestion and greater opportunity for drivers to notice their surroundings? Are flashing lights necessary in such settings?

This is debatable. Under these conditions, wearing brightly colored clothing might be enough to get a cyclist noticed. Even in the dark, light clothing stands out in a car’s headlights. And, reflective accents or vests can catch a driver’s eye.

In essence, multiple methods exist for making a bicycle visible. Yet, the flashing white lights have continued to grow in popularity, more than any other visibility creating method.

Despite the success of these lights in gaining the attention of everyone facing the bicycle where they are mounted, a downside exists. Strobe lights can cause some people to have seizures.

Contrary to popular belief, not everyone who suffers from seizures is sensitive to flashing lights. And some individuals who are not prone to having seizures can become dizzy or possibly have a seizure, if they are unusually sensitive to bright, flashing lights.

This concern has been cited as a reason for reducing the use of flashing bicycle lights. While these concerns are well-intentioned, the fears of their proponents may be overblown.

There is a big difference between seeing a small flashing light at a distance and having a large flashing light or several flashing lights directly in front of one’s eyes. Individuals with seizure disorders know what triggers their seizures. And, they try to avoid those things.

It really isn’t very difficult to look away from a small flashing light on the front of a bicycle. And, the percentage of people with seizure disorders who are sensitive to flashing lights isn’t extremely high. Therefore, the odds of a person with this disorder coming into contact with a bicycle using a flashing light is fairly small. And, yet, these lights are frequently referred to as “seizure-inducing.”

What it boils down to is that these lights have been colloquially connected with a medical condition because some people are irritated by them. Rather than referring to the lights as annoying, when they would prefer that no one used them, they imply that these lights are doing a disservice to those with a particular medical problem.

It’s a way of making something they dislike look unacceptable without coming right out and saying so. Nonetheless, cyclists should try to regard the use of these lights as a positive thing, even if, on an individual level, they don’t like them.

As irritating as these lights may be, they make the cyclists using them feel safer. Feeling safer means that they are more likely to ride their bikes on the roads. This increases the total number of bicycles on the roads, which benefits everyone — even though some drivers refuse to admit that this benefits them too.

With so many would-be cyclists citing fear of riding in traffic as a primary reason for not using a bike for transportation, we should be more forgiving of safety promoting behaviors which make cycling seem less dangerous. After all, how many times have we heard a driver use as an excuse for hitting a bicycle: “I never saw the bicycle.”

How likely is it that this excuse will be believed when the bicycle in question was sporting a blinding, “seizure-inducing” light? Not likely. More likely than not, the driver wasn’t paying attention or was driving recklessly.

On more than one level, flashing lights provide safety — by giving a cyclist a psychological edge and by creating a situation where a driver can’t claim to not have seen the bicycle he hit. Momentary irritation on the part of oncoming traffic is a small price to pay for a cyclist’s peace of mind and for potentially saving her life.

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16 Responses to Seizure-Inducing Bicycle Lights

  1. JonT says:

    I haven’t looked at the literature on flashing lights triggering seizures, and a quick Google search was inconclusive, so I won’t comment on that, other than to note that it’d be worthwhile to have some stats on just how common or rare it is. Obviously if it were extremely common there’d be more info on it.

    But from my own experience, the blinking lights often give me a bit of a headache, and will intensify one that I already have — even if the blinking light is on my own bike or a bike behind me and all I’m seeing is the reflection on the pavement. In addition, I find it to be a distraction. The blinking, whether observed directly or reflected of the road, tends to grab my attention to it, and away from other things on the road.

    You write “It really isn’t very difficult to look away from a small flashing light on the front of a bicycle.” That may be true if all you want to do is look away from it, but if it’s on a bike in the oncoming lane and you’re driving a vehicle, it’s quite difficult to get the blinking light out of your field of view while still getting a good view of the road and other vehicles in front of you.

    So now we’re talking about something that I’ve called distracting and you’ve (twice!) described as “blinding”. Are we certain that this is something that will reduce the chance of accidents? I’m pretty sure the answer is “no”, and would require something awfully persuasive (e.g. a scientific study) to convince me otherwise.

    But there is a solution. Just set your headlight to be constantly on, instead of blinking. People are accustomed to seeing a bright, steady light on vehicles, and will avoid it. From a distance, you’d probably look like a motorcycle or a car with a broken headlight.

    Blinking lights had their place ten years ago when LED technology was less mature and headlights were not very bright, and needed to blink to be noticed. Today’s bright headlights should be just turned on, and shouldn’t blink.

    • IsolateCyclist says:


      I agree with much of what you’ve said. I don’t have statistics available about the percentage of patients whose seizures are triggered by flashing lights, but from work I’ve done in Neuroscience, which included interactions with Neurologists, I understand that this trigger is seen in a subset of patients who have a particular type of seizure. So, it is not seen in all seizure types, and even in the types where it can be a problem, only a portion of the patients experience it.

      Headaches are another story. Some people do get headaches from flashing lights, but ordinarily the flashing would have to persist for a significant amount of time, like what you experience when your own bike light is flashing during a ride. This would only be a problem for the cyclist, not oncoming traffic, since they would only see the flashing light for a moment.

      As for looking away from a flashing light, I have no trouble doing this either in my car or on my bike. When a flashing bike light is far away, it is miniscule in relation to the overall scene. As it gets closer, you only have to look straight ahead and slightly to the right for a minute until the bike passes. Looking towards the right of the road for a moment is unlikely to pose any danger for a driver or a cyclist. It is something cyclists and drivers do all the time when oncoming motor vehicle headlights are blinding them.

      Your point about the light being a distraction may seem like a negative to you, but it validates the reason many cyclists choose to set their lights to flashing mode. Drivers’ eyes are attracted to the light, and away from other things they might be looking at otherwise. They can’t help but notice the cyclist — and this is what makes some cyclists feel safer.

      If someone has a very bright (usually expensive) headlight, which is highly visible at a distance, then they might be able to achieve the same affect as the flashing light method in getting noticed. But, I don’t think we should demand that everyone use a steady beam because, as I’ve already said, some cyclists feel safer with a flashing light and they might not be willing to ride in traffic otherwise. If they are more comfortable with a flashing light, they should not be asked to change their ways on the pretext that their actions are causing difficulties for people with certain medical conditions. Instead, the adequacy of today’s bright lights in making cyclists visible can be emphasized — as you’ve suggested — and hopefully these cyclists will agree. By keeping the number of people who use flashing lights low, we can adequately accommodate everyone’s point of view.

  2. JonT says:

    I think you’ve missed my point about distraction. Yes, the cyclist is highly noticeable, but the driver’s attention may be distracted enough by the blinking that he doesn’t notice some road hazard and hits something (or someone) else. Or he swerves to avoid something he didn’t notice until the last minute (due to being distracted by the blinkenlight), and the cyclist is still put in danger.

    And my point about the advances in LED technology is that bright headlights are no longer very expensive. The very same “blindingly blinking” headlights that folks are using right now are bright enough for cyclists to be seen very well when set to steady mode. I’m not asking anyone to buy new equipment, but to change a setting on their existing headlights.

    Your comment re headaches does not match my experience. It happens to me pretty quickly, especially if I already have a mild one. It’s not excruciating, but the fewer distractions I have when I’m on the road, the safer I feel.

    Which brings me to perceptions of safety. I have chatted with a few cyclists who have had very bright blinking lights that were causing me distraction and distress, and indeed that’s what they’ve said: that they feel safer that way, that they’re less likely to not be noticed. But is there a disconnect between perceived safety and actual safety? I think there very likely is, and education is key.

  3. Lee Hollenbeck says:

    Couple of comments here. When I am driving my car, the bikes I notice the most have blinking lights. I like to have 2 handlebar lights, steady and blinking. Also my new cygolite metro light has a nice feature, a steady light with a momentary flicker. Works great.

  4. James Haroldson says:

    There is scientific evidence that suggests a flashing light is harder for the human eye to judge in terms of location and distance than a fixed beam equivalent.

    ‘A target moving physically in discrete spatial jumps could elicit smooth tracking eye movements in practised observers, but this tracking was increasingly interrupted by saccades when the temporal interval between the spatial jumps of the target was greater than 150 msec.’

    “Smooth eye tracking and the perception of motion in the absence of real movement” by Morgan and Turnball, 1978

    Also some of these lights are now the equivalent of a camera flash bulb going off repeatedly. Ask any film star how disorientating that can be.

    White flashing lights do disorientate which should not be the aim of a cyclist.

    Oh by the way I am an epileptic so I’d like to correct a few assumptions made here.

    Firstly Epilepsy is a disability (very important thing to note).

    Not all epileptics are sensitive to strobes but these who are have varying degrees of sensitivity.

    For myself I am not usually at risk of a seizure from flashing lights but it does cause severe discomfort and can increase the affects of disorientation plus induce headaches.

    Normally the feeling when I encounter a bright flashing light is the equivalent to being punched in the face every time the light flashes. It’s not pleasant but it’s also not necessary for a cyclist to inflict this on me when they can use a fixed beam light instead.

    The author suggests its not difficult to look away from the flashing light. Well what if that light is on a bicycle riding towards me?

    Are people meant to close their eyes or not look in the direction that they are travelling whilst the offending light is in view (which can be for up to 30 seconds)?

    Wouldn’t averting ones eyes whilst driving a car or riding a bike be dangerous? What if there are several bikes with these lights? (which is often the case) It’s not exactly safe to travel whilst not looking where one is going.

    Another point to note is that epilepsy is something that can be triggered suddenly in someone who has never shown any symptoms before. It’s very difficult for that person to avoid things that may trigger seizures when they don’t even know that they are prone to them. Imagine a scenario where a person has their first seizure whilst driving a car. Could be dangerous.

    The notion that people who know about their condition ‘try to avoid these things’ is also not practical. Where I experience cyclists with flashing lights is mostly on pavements which are shared cycle routes or from cyclists on the side of the road whilst I am walking on the pavements. Are you suggesting that epileptics cannot walk around the streets at night? I would have to give up work during the winter so that I didn’t encounter any cyclists on my way home. Sounds like discrimination against people with disabilities to me.

    One particularly bad experience that I had with cyclists was when a large group of around 100 cyclists (enough to form a decent peleton) staged a mass protest in the area that I live. It appeared to be some kind of ‘own the streets’ type protest held at the 6PM rush hour (obviously without the local authorities being informed about it) in the winter when it was dark. The cyclists occupied the entire road blocking the traffic and came riding towards me as I was walking home from work. Lots of them had bright flashing lights and it was incredibly painful. There was no way that I would have known about that in advance in order to take any necessary action to avoid it.

    Also many epileptics are in control of their condition and have been for many years. There are legal restrictions for safety reasons for people who have regular seizures or have had one in the last few years in terms of not being allowed to operate a motor vehicle and not being allowed to do certain jobs.
    These restrictions do not apply to someone who has previously had seizures but hasn’t had one for a number of years. By cycling with unnecessary flashing lights, you run the risk of triggering a seizure in someone who has not had one in many years and thus affecting that persons life for a considerable amount of time in the future.

    It’s not just epileptics who are inconvenienced by these lights, many pedestrians and drivers who share the same space as cyclists (often not at their own choice) have complained about the flashing lights.

    There is no proof that flashing lights are safer but there is proof that they can cause confusion, disorientation and discomfort.

    It doesn’t take much effort to switch to a fixed beam setting but it does cause a lot of problems for other people when a cyclist uses a flashing light.

    It’s all about consideration for other people.

    • IsolateCyclist says:


      While I’m sure that your comment is intended to protect people with epilepsy, I feel I must respond because I believe it has the opposite effect. First of all, here in the U.S., epilepsy is only considered to be a disability if it can’t be controlled with medication. In most cases, it is seen as an illness, a treatable illness.

      As you mentioned yourself, most people with epilepsy, including my own family members, can be treated successfully. Further, your experience as one person with epilepsy does not represent everyone with epilepsy. These are your own experiences, as one person, and your own opinions.

      The doctors I have worked with have been doing epilepsy research for many years. During that time, they have seen thousands of epileptic patients. While you may be unable to look away from a small flashing bicycle light, and may feel discomfort or disorientation from looking at it, many people with epilepsy do not, and they would be offended at your suggestion that they are unable to do so. Please be aware that many people with epilepsy do not consider themselves to be “disabled” and less capable of doing things than people without epilepsy.

      As for the danger of looking away from a flashing light while driving, people do this all the time when driving and cycling due to very bright automobile lights. I often ride my bike on rural roads where cars routinely use their high beams. Even at a distance, I am blinded by the light and cannot look straight ahead. To avoid crashing, I put my left hand over my eyes to reduce the glare, and look downwards so that the headlights are not shining directly into my eyes.

      Sometimes the driver notices me and turns down their headlights. Other times they do not. I have never crashed my bike because of the blinding headlights or from looking away from the road until I pass the car. The same is true when I drive my car. If someone is headed towards me with their high beams on and forgets to dim them, I look towards the side of the road so that I am not looking directly into the bright light. I have never crashed my car or even come close to having an accident from doing this.

      Your theory that people who have never had a seizure before might have one triggered by a flashing bicycle light is very farfetched. While it’s not impossible, it is so improbable that one would have a much greater chance of being struck by lightning than have this happen to them. Lightning is also dangerous, and it can kill people. So maybe we shouldn’t let anyone drive on the odd chance that they might be struck by lightning for the first time while driving and cause a serious accident.

      With respect to your assertion of “proof” about flashing lights causing confusion, disorientation and discomfort, I would say that if any exists, it is mostly anecdotal. One or two small research studies confirming this doesn’t prove anything. You have to test these things on large numbers of people for the results to have any meaning.

      There is anecdotal evidence that flashing lights are safer in that they attract attention to an approaching cyclist. I use a flashing light occasionally, in certain settings where I believe I might not be seen in time otherwise. In my own experience, drivers not only see me, but they give me more room and are less likely to cut me off when turning left than when I don’t use a flashing light. So, I have fewer problems with drivers when I use a flashing light. This enhances my safety.

      Now, the main reason I have written such a long comment is that I, and many of my friends and colleagues, have spent a lot of time advocating for people with epilepsy, particularly with respect to driving. Because of the type of arguments you have set forth, which paint epileptics as fragile, disabled people who might have a breakthrough seizure at any moment, many people around the world do not believe that anyone who has or had epilepsy should be allowed to operate a motor vehicle. It’s words like yours that keep people with epilepsy from driving.

      Just because someone has had seizures at some point in their life does not mean that a flashing bicycle light will trigger a seizure and cause them to lose their driver’s license. This will happen so rarely that it is not even worth considering. Other things such as sleep deprivation or acute stress are far more likely to trigger a seizure after one has been seizure-free for a prolonged period of time. These things can be monitored and avoided by people with a history of seizures to prevent a recurrence.

      One last thing I want to comment on is your obvious dislike for cyclists. Do you think that this bias might color your view of flashing bicycle lights? After all, if your theories are wrong, more cyclists could die on the roads as a result of not being visible to motorists. Does this worry you at all? Or are you only concerned that the small subset of people with epilepsy who might experience discomfort or seizures from the flashing lights be accommodated? In other words “consideration for other people” should mean consideration for all people, not just one group of people.

  5. Sean says:

    Actually, they induce seizures. Hopefully they’ll be banned

  6. Angel in Seattle says:

    These bike lights gave me seizures thus morning. I actually found your site googling them to see if other epileptics like me have had this problem. While it may seem like no big deal (an epileptic having a seizure) many of us can go ten years plus without a seizure. Once you relapse you immediately lose your drivers license and in my case potentially your job as I depend on mine to make a living. You also go get to spend the day at the neuro trying to find new meds. It’s a huge life altering issue. I’m all for rider safety lord knows driving in a car is dangerous enough with some of these awful drivers let alone being up against these careless drivers on your bike! There just has to be a better way that doesn’t cause potentially dangerous situations like seizures while driving. Stay safe

  7. Pedestrian says:

    Well, for one thing, blinky lights are illegal in many states. I know they are in mine:

    Though this isn’t enforced.. it well should be. If one does proper research into this subject (which will require you to look outside the US where bike riding is more prevalent) it will be shown that many countries have banned the blinky lights with good reason and have studies to back them up. This was borne out in a Dutch safety study which concluded, “bicycle lights should not flicker.” Europe, in particular the Netherlands and Germany, are at the forefront of bicycling as a general rule. Thus, it’s no surprise that this was a Dutch study. It’s also no surprise that in Germany, traffic regulations prohibit blinking bicycle lights altogether.

    A blinking headlight not only means motorists can’t ascertain your precise location, direction of movement, or distance, they also get disoriented and may suffer from the dreaded moth effect in which drivers are actually attracted to your blinking light.
    Also, here is an in-depth European study on bike lighting and safety, in which they note the following about flashing lights on Page 31 (after a diagram and additional info):
    It can be concluded that flashing bicycle lights are not necessary for a good conspicuousness.
    Flashing also has the following general disadvantages:

    • It may confuse others, for example confusion with the lights from an emergency vehicle
    • It may irritate others
    • It makes other traffic participants less visible
    • It makes it hard to judge the distance and path followed by the cyclist

    So, there seems little use for flashing and certainly should not be promoted.

    Here’s a good article from a bicyclist in Seattle on the issue:

    As a pedestrian who doesn’t suffer from epilepsy and who’s had only a handful of migraines in my life-time (all due to strobe lights).. I instantly get dizzy, disoriented and nauseous when I have them approaching me on my walk into work. This has led to migraines on several occasions now. I’m clearly not the only one. Several people have mentioned that they too experience this and have had to change their lives around (times of day to go to work, etc.) specifically because of the blinking lights.

    People, there’s no proof that you’re any safer with your blinking lights and more proof that you’ll “dazzle” other road users and make it difficult for them to judge distance, your speed or direction of travel. Just use a good, steady light of good strength and keep to the rules of the road. You and everyone else will be far safer for it. Please let’s make it a comfortable journey for everyone transporting in our cities.

    From a fellow bicyclist and pedestrian.

    It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.” – Mark Twain

    • Mark says:

      Boy, you can’t read at all. Your reference to Washington state law says that blinking lights are LEGAL on a bicycle. HAHAHA! The word “except” in section (3) allows it. Sorry about your epilepsy.

  8. Migraine sufferer says:

    I suffer from chronic migraines and one of my triggers has always been flashing or flickering lights. These strobes have triggered many a migraine for me. It’s difficult to drive when I’m having dry heaves and it ruins the rest of the night for me. I really wish people would just set them to On. They’re plenty bright. There’s no need to have them strobe.

  9. Mark says:

    Boy, you can’t read at all. Your reference to Washington state law says that blinking lights are LEGAL on a bicycle. HAHAHA!

  10. Mark says:

    My comment was to Pedestrian.

  11. Mark says:

    My bad. The exception only applies to tail lights. Sorry.

  12. Laurie says:

    The conversation and reference is to blinking HEADLIGHTS and is noted so in the comment. The law is very specific in that it mentions JUST taillights, not headlights.

    “Flashing lights are prohibited except as required in RCW 46.37.190, 46.37.200, 46.37.210, 46.37.215, and 46.37.300, warning lamps authorized by the state patrol, and light-emitting diode flashing taillights on bicycles.”

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