I spent a fair bit of time riding in the lane, in traffic. In this situation, it seems that a brake light would be very useful: It's not always obvious when the vehicle ahead of you is slowing down, and I don't want to be rear-ended by someone who doesn't notice me slowing.

This intuition does not match reality. I was not able to find any bicycle brake lights that seem really ready for prime time. This is what I was able to find:

  • Q-Lite Multi — Apparently available from just one vendor (TerraTrike). Not mentioned on manufacturer (Q-Lite) website.
  • Maxxon — Available on Amazon, but poor reviews suggest it does not detect deceleration well.
  • Revolights — Complicated spoke mounting system; unclear drivers will interpret it properly.
  • Velodroom — Not yet available (pre-order only).
  • LucidBrake — Perhaps the most promising of the bunch. Apparently available only direct from a not-so-great website.

The first uses a brake handle-mounted switch. The others use accelerometers to detect slowing.

None of the major bike light manufacturers seem to offer a brake light.

My question is, what's the disconnect? Am I misjudging the value of brake lights? Is there some challenge that makes them hard to offer for bicycles?

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    Since bicycles have never had brake lights, I seriously doubt that drivers would see them for what they are. Commented Nov 16, 2014 at 0:20
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    Until recently any lights on bikes were either expensive or unreliable - or both. Until very recently brake lights would not have been practical for a majority of bikes and legislation would have been ineffective at enforcing it in most countries. Given the difficulties, the market was too small for it to be worth while manufacturing for it - there has always been products availble, but they have never been popular. .
    – mattnz
    Commented Nov 16, 2014 at 2:03
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    Expanding on Matt's comment: daylight visible LED lights that are small enough and efficient enough to fit on a bicycle are a pretty new thing - the last couple of years. Before then they were heavy and expensive. But people still made and sold brake lights for bikes. Just hardly anyone used them, as they were toys.
    – Móż
    Commented Nov 16, 2014 at 2:35
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    They're not common because they're inappropriate. Bicycles are not motor vehicles. Commented Nov 16, 2014 at 17:18
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    @whatsisname It is stupid comments like that that cause drivers to force cyclist off the road everyday! A high performance cyclist can easily reach speeds above 20mph, which can be fatal in an accident. How does a motor affect safety or braking requirements?
    – Aron
    Commented Nov 24, 2014 at 10:49

11 Answers 11


Summary: it's hard to make a light that reliably turns on only when the brakes are used. Most cyclists who want brake lights buy rear flashing lights because they're cheap and ubiquitous.

Ignoring cost, to work well a brake light on the back of a bike would need to be paired with a constantly on, non-flashing light, purely so that people who saw it would recognise it as a brake light. Otherwise it's just another blinking light on a bike. Then it needs to be daylight visible, or no-one will see it.

From my experience with rear lights, 200 lumens is about the level you'd want from a brake light. My always-on dynamo rear light is about half that and while it's visible it doesn't really stand out. In other words, it makes the bike more visible without being too bright. But for a "hey, I'm stopping" light, you want more than that. So the combination of a 200-500mW always-on light with a 1W or 2W "BRAKES!!!" light would probably work pretty well.

Unfortunately most super-bright LED rear lights are designed to overdrive the LEDs in short flashs, but for a brake light you want a solid 2-5 seconds of on time. Which means bigger, more expensive LEDs. And also a bigger, heavier battery to drive them.

The sensors are also challenging. SeeSense have done a lot of work on accellerometers in bike lights and from using their light, braking detection is ok but not brilliant. If I hit the brakes to reduce the impact of hitting a pothole, for example, the light seems to got into "holy shit" mode instead of braking mode 90% of the time. Which might be ok for a brake light, 5 seconds of braking mode in that situation is fine. But it means that I'll get 5 seconds of braking mode when I bunnyhop a curb or bounce a speed bump too. Which isn't really "braking" as I think of it - I'm definitely not slowing down at that stage. So you probably want sensors on the brake levers as well (the accellerometer is built into the CPU that runs the lights). Which means wires and fiddly mechanical bits. I dunno, that seems hard to me, you have to cover road bikes with integrated electronic shifting right down to basic V brake levers. Sounds expensive.

To get an idea of costs, look at some of the KickStarter bike lights. It seems to cost about $100 to get a light to market. Which means hardware costs of about $25. If we double that because we're using, say, two 18650 LiIon batteries (18Wh) instead of one, CR123/16340 battery (half-16550, 4.5Wh) and a 0.5W RED LED as the primary light plus a pair of 1W LEDs as the brake light... ok, maybe triple it. So you're looking at a light that will cost about $200-$300, assuming the sensors are cheap and reliable. Cheap means pure accellerometers, like the last light in your list.

Which makes them "something is happening" lights... just like any other blinking light on the back of a bike.

  • Disagree with your points about the physics and electronics. Firstly a large LED, its pretty cheap, alibaba.com/showroom/5-watt-high-power-red-led.html. Secondly, sensors, add a switch on the Bowden cable, cheap. Thirdly, unless you like to simulate a hill with your brakes when cycling, you will likely only have your brake likes on for about 1 minute or 2 on your whole ride, a 18Wh battery will give you 2 hours of usage...Bit OOT; a pair of AAA with a super cap will more than suffice. I would put the BOM ~ 5USD. RRP 20 cuz capitalism!
    – Aron
    Commented Nov 24, 2014 at 10:58
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    @Aron: Two 5W LEDS is $5.60 from that seller... you also need a case, battery, controller, waterproof microswitch plus cable harness.
    – Móż
    Commented Nov 24, 2014 at 21:18
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    Controller? It's controlled by a switch for Pete's sake... Not everything needs an Ardueino to power it. To be honest I could build you a low resolution single axis accelerometer out of two pegs a rubber band and a ball bearing.
    – Aron
    Commented Nov 24, 2014 at 23:41
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    You are attacking me on a BOM over a few dollars when you are orders of magnitude off.
    – Aron
    Commented Nov 24, 2014 at 23:42
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    @Aron I'd be quite interested to see your proposed BOM for such a system.
    – nhinkle
    Commented Nov 24, 2014 at 23:53

It's not common in Europe either, but it's getting less rare it seems like.

A quick browse in one of the larger German online stores (Rose) shows that several of the larger bike light makers (Busch & Müller, Axa ...) now sell dynamo-powered rear lights with brake light functionality.

All lights work in the same manner : They are fed rectified but not smoothed DC from the front light, which means that the DC is overloaded with a ripple from the front hub dynamo that is exactly proportional in frequency to bike speed. When the frequency drops fast enough (because of stopping) the light gets brighter. Quite elegant in a way. I haven't tried it, though.

It probably helps for marketing it that most commuting bikes here, especially in Germany, comes with hub dynamo and dynamo-powered (LED) lights both front and rear. I don't know how many find it useful "seriously" and how much it's just a novelty.

In addition, many velomobiles are sold with serious brake lights, often connected with a sensor on the brake lever (equivalent to the way it work on motor vehicles).

  • 1
    That's a very elegant solution! At least for people with dynamo lights. It probably also helps that bikes in Germany don't usually have flashing lights, so the change in brightness is much more obvious.
    – Móż
    Commented Nov 18, 2014 at 21:22
  • Doesn't that add significant cost to bikes in Germany? Commented Nov 19, 2014 at 4:47
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    Carey - if you haven't noticed, Germans tend to believe that better safety and performance are worth paying more for.
    – RoboKaren
    Commented Aug 26, 2015 at 12:58
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    @CareyGregory: Does the lighting add significant costs to cars? A new front wheel with hub dynamo of decent quality is around 40e (dynamoless wheel is ~20e), and set of lights (front+rear) starts from around 10e. So, the difference in the cost is about $35. Judge for yourself is it significant enough or not. Commented Oct 22, 2015 at 12:05

Bicycle rarely use harsh braking, even if you have enough braking power, you wouldn't use it because you probably know how easy it would be to come off the bike using harsh braking. So the benefit of a signal saying: "Hey I'm stopping, u better brake and be ready to stop" is minimised.

As a motorist, I noticed that cyclist rarely ride in the middle of the road, and in front of a car, then suddenly brake-check me... Rather more often, other motorist did brake-check on me.

For me as a cyclist to motorist, I am rarely stupid (enough) to hold up a fast moving 'object' behind me, leave alone braking. As a cyclist to cyclist, there is no need to tailgating another cyclist. I only did tail-gating when riding in my club where people know that no matter what happen, avoid harsh braking.

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    This is a valid point. A) Bikes are rarely going that fast, especially in traffic -- the "delta" velocity between moving and stopped is small. B) Most cyclists are very aware of vehicles behind them when cycling in traffic, and very wary of making sudden moves. And when riding in a draft line one gets better info by observing the feet of the cyclist ahead. Commented Nov 16, 2014 at 14:15
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    With a 20mph zone now covering most of a hilly city around here the situation changes: Bikes and cars are going at roughly the same speed (though car drivers often don't realise this before they act) and freewheeling downhill means the pedals aren't going up and down.
    – Chris H
    Commented Nov 19, 2014 at 16:10
  • The arguments still valid for bicycle, you would not (for the purpose of commuting) flying down a hill then brake harshly to avoid sudden hazard. You probably flying off the bicycle braking, which is more likely than being hit by a car from behind.
    – Nhân Lê
    Commented Nov 24, 2014 at 3:02
  • Also, cars are often in a line of moving traffic where you follow the car in front of you at fairly high, constant speed. These are the situations where brake lights are most useful, and where rear-end collisions are common. Bicycles are in a different situation and you rarely get rear-ending (and when somebody drives into a bike from behind, it's rarely due to braking, but misjudged overtaking or distraction). So brake lights make much less sense for bicycles.
    – uUnwY
    Commented Aug 3, 2015 at 20:30
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    @ChrisH I actually meant why cars need brake lights, sorry that I didn't make that clear. If cars never reached speeds higher than a bicycle, we might not have regulations requiring brake lights... But you make a very good point that bicycle brake lights would not be understood, especially as nowadays people already have all sorts of lights with most complex flashing sequences.
    – uUnwY
    Commented Aug 3, 2015 at 21:10

Cost would have to be the biggest obstacle. Several hundred dollars to retrofit a system, assuming it is impeccably reliable, might be an insignificant expense to someone riding a $7,000 titanium custom bike, but it's an insurmountable sum for someone riding a Craigslist beater bike because it's what they can afford.

For new bikes, let's presume that mass production would take the cost down to $100. Once again, for the person buying a $6,000 cromoly lugged custom bike, it's nothing to tack on $100. For the person shopping at a Big Box Store, they aren't going to tack on $100 for a brake light when they're only looking to spend $150 to $250 on a bike.

If I set aside cost, I would have to express my skepticism that a brake light offers any significant improvement in safety. I run 10 lights on my commuter: 4 tail lights, 2 head lights, and 4 spoke lights. I have my eye on additional lights to improve visibility--head, tail, and side--but brake lights aren't even on my radar.


Apart from the complexity already described, it's arguable that bikes are almost always going slower than cars, who seem to be the main following vehicle intended to notice brake lights. A car seeing a cyclist ahead will almost always need to slow down or overtake. If the cyclist is braking they just need to do so a little sooner. Coupled with being able to see when a cyclist is pedalling or not, this gives brake lights much less value on a bike. If rear light can go brighter without dazzling others, some cyclists would want to have it brighter all the time.

(IIRC, this is the gist of a suggestion in a recent CTC Cycle magazine article).


In term of safety, I think signaling intention to turn would be a higher priority than signaling braking - the benefits of signaling braking are questionable as many have pointed out above, but turning left (in a right side driving country) or right (in a left side driving country) is an accident prone maneuver even when bicycles signal and move over to the left (right) in advance of turning.

Because cars do not expect turn lights, turn lights are probably not a safe alternative to hand signaling. But because hand signaling requires a hand, it affects stability of riding - hence a good solution would be a third arm which popped out and had a light on the end.

However, in my experience and in the area where I currently live, signaling often leads to cars accelerating dangerously to get around the bicycle before it turns, hence somewhat negating the safety benefits of turn signaling.


I ride my bike to work every day and also ride mountainbikes in my free time. I never had the feeling that cars might crash into my rear end, right turning cars (we're driving on the right side) and opening doors are a larger problem that cannot be fixed by tail lights.

However, there a another light missing from the list above - from German manufacturer Lupine. It charges via Micro-USB, which I like. It's called Rotlicht and has an acceleration sensor to see whether you're braking: Rotlicht Here's a review on mtb-news.de (in German though).

  • 1
    The "review" is just a repeat of the marketing and they don't comment on whether the brake light feature actually works. I have my doubts about accelerometers accurately detecting braking based on my experience with the SeeSense lights so it would have been good if that magazine had at least tried the light.
    – Móż
    Commented Oct 21, 2015 at 21:29

Seems to me that these days the easy solution to this problem would be either to add an accelerometer to the light or if the bike had a Bluetooth or ANT+ speed sensor to use the signal to detect deceleration and then use that to run the brake light.

I don't know of any lights that do that (but I haven't been looking since I'm using the B&M dynamo powered brake light), but it seems like it shouldn't be too expensive to add the functionality to a battery powered light – at least not compared to either a dynamo system or the costs and hassle of adding a brake light switch.


Maybe not too visible to cars, but I think the following brake light is ideal if riding in a pace line on a group ride, for the price and weight it can't be beat. If something comes up you might need both hands on the brake levers and can't signal to riders behind.


It is triggered by the back brake squeezing its lever when the back brake is applied.

  • Interesting idea - as long as it doesn't replace the proper rear lights!
    – Criggie
    Commented Oct 9, 2016 at 21:28
  • Could you possibly edit this so it at least pretends to answer the question? Also, if you're affiliated with the product you're promoting you must disclose that.
    – Móż
    Commented Oct 9, 2016 at 21:34

What do you mean "It's not always obvious when the vehicle ahead of you is slowing down". Cars have brake lights.

For bike to bike communication you say slowing or stopping and hold your left hand in a down position.

For bike to car the car is typically going faster. Here is my flashing light - I am a bike - please don't run over me.

Car to car they have lights because they have windows, stereo, AC, and kids in the back seat. They need lights to communicate.

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    Stop signal described only applies to North America. Other countries have different signals.
    – mattnz
    Commented Nov 16, 2014 at 1:58
  • @mattnz OP is from NM - that is North America. If you are in another region I hope you have a standard.
    – paparazzo
    Commented Nov 16, 2014 at 2:14
  • Agree or not, I don't understand the downvotes. Commented Nov 19, 2014 at 4:45

I agree. Not an easy job. Brake lights must be waterproof, including switches. Operation in extreme temperatures is also a challenge. Got to work in very hot weather in summer and subzero F temperatures in winter. I have had some Chinese made lights that were very temperature sensitive and not waterproof. Not useful beyond spring weather. Chinese skimping on "automotive temperature range" and "military temperature range" components. These cost money.Chinese makers are usually not going to spend the money, skimp on components instead. Small inventors will quickly run into price fixing. Kickstarter can help, but realistic cost estimates of neeeded top quality components need to be listed "up front". At present, 2W LEDs give plenty of visibility. NiteRider Solas tail light is prime example. Circuitry controlling LEDs seems to be a problem. Not taking brake light function very seriously as yet.

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    Welcome to Bicycles @James. The internet will not out of space if you write full sentences and insert some white space. Please edit your post to make it more readable :-)
    – andy256
    Commented Jan 4, 2015 at 12:16

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