I'm familiar with bicycle brake lights but not sure why they aren't more common? What is the public perception, if any? Or not the public but more serious cyclists like we find here? There are a plethora of them on Amazon. Benefit seems valid. Thoughts or alternatives, especially.

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  • I have them in my velomobile (as do most who ride VM) but will not spend money on them for my other bikes, as I do not ride those in a group.
    – Willeke
    Feb 10 at 20:34
  • Mattnz - in the Netherlands more people ride per capita than anywhere in the world. More than 1 bike per person. Brake lights here in the US warn cars behind you that you are stopping, esp. in a panic stop. brake light goes on!! ..they'd never know in time to stop with a regular light. kid runs in front of you.you hit the brakes, car behind doesn't know, BAM. In Netherlands, could that ever be an issue?? It is here, at least in CA. thx Feb 10 at 21:48
  • @FredGoldfarb this is a good question and you've earned some upvotes for it. There is a previous question that asks the same thing, so if this gets closed as a duplicate, it's not a bad thing so don't take it personally.
    – Criggie
    Feb 11 at 7:08
  • Bikes have a side-advantage in that there is nothing between the rider and the world. So you can shout successfully and be heard. That's not generally possible with a car.
    – Criggie
    Feb 11 at 7:28

2 Answers 2


My sense of why bicycle brake lights are not yet common, based on working in a couple of local bikes shops the past two years:

  • Major bike brands have longer business cycles than Amazon brands and have yet to respond to the innovation of accelerometer brake lights, though some makers, for instance Kryptonite, have recently introduced them
  • Many cyclists already have an older working light set they're not yet ready to replace
  • Lever actuated brake light systems definitely are more common on ebikes, which usually have wiring paths and power systems for integrated lighting, but are harder, more costly to retrofit onto existing builds, so there has been very little product development in the space
  • Bikes are allowed to be built without them, so a market in a perpetual race to the bottom nobody is going to spec the part

I have a Tern GSD cargo bike with a brake light. I don't know if it makes a lick of a difference to anybody else, but I LIKE IT.

  • All these points only concern e-bikes. Ordinary bikes would need some complicated sensors that would trigger those brake lights. Feb 11 at 8:23
  • @VladimirFГероямслава the first point no. Some batteries powered lights are equipped with accelerometers that will change the brightness if a sudden deceleration is detected.
    – Renaud
    Feb 11 at 8:25
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    Accelerometers have nothing in common with using brakes. Automobile brake lights do not and should not illuminate when a car decelerates when climbing a hill. Bicycle lights triggered by accelerometers would illuminate all the time and would be just noise, not useful information, and would get ignored very quickly. Feb 11 at 8:26
  • @VladimirFГероямслава it depends how the brake light is configured/calibrated. It's not rocket science to ignore signals from the accelerometer if they are below a certain threshold (or even compare against the last minute to only consider sudden changes). Yes, it's not as good as a proper brake light, but nobody here claimed it was...
    – Renaud
    Feb 11 at 8:47
  • @Renaud But this simply not a brake light. Motorcycles or motorized scooters, which are closer to bicycles than cars, do not illuminate their brake lights when the bike decelerates. It illuminates when brakes are used. When a motorbike is fast and the throttle is released it can decelerate quite fast due to the high drag. The more if it is uphill. But the brake light is not supposed to shine. Feb 11 at 9:44

Bicycles are primarily intended to be simple machines. The more "stuff" that goes on it, the less-simple it gets.

Ebike technology makes it less onerous to pedal around with "not-mandatory" items so I'm unsurprised active brake lights show up there more than regular bikes. Also, many ebikes have sensors to cut the motor/assist when a brake lever is activated, so its only wiring plus a light fitting to provide a braking lamp.

For a regular human-powered bike, every bit of complexity adds up. For brake lights, sensing that the brake is on needs to measure movement of the cable or pressure in the hydraulic line, and there's two completely independent brakes on normal bikes.

Any brake light would have to "fail-safe" and run minimal risk of stopping the brake from working. So it would likely involve non-contact sensors of some sort.

Additionally, some bikes have coaster brakes, or fixed-gear bikes that have nothing but the rider's leg to brake. Fitting a brake light sensor to those setups would be difficult.

Practically, if I'm riding with someone else right on my wheel, then I trust them to look out and ride "properly"

More generally, brake lights feel like a technical solution to a road design problem. Make the roadway wide enough that cars and bikes never share a lane. Make the bike lanes wide enough that passing another bike doesn't require moving into the vehicle traffic lane.

And then.... I remember that the automotive seatbelt received similar scorn. As did airbags, indicators, rearview mirrors, cycling helmets, and the safety bicycle itself.

Picking seatbelts as an example, they are an inconvenience and a faff and an extra cost, but data clearly shows they save lives over non-seatbelted accidents.

The way to find out if bicycle brake lights make a difference is to have a whole lot of them attached to bikes in an area, and see if the accident rate changes significantly over a test period of a year.

Fitting one to a bike isn't enough of a sample to show effect reliably - you'd likely need at least 100, with 500 being better and maybe more. A qualified independent statistician would be needed to analyse the results to give you a "confidence level"

With that information one could potentially support a decision to legislate such items. This is how New Zealand and Australia have ended up with mandatory bicycle helmet use.

  • "not-mandatory" is a terrible phrase - I'm looking for something more than "optional" but less than "mandatory"
    – Criggie
    Feb 11 at 7:26
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    Non-essential? Non-critical?
    – MaplePanda
    Feb 11 at 7:39
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    The mandatory bike helmet laws are there because the people in power believe the promotion by the helmet makers, this can in the future also happen with brake lights. That does not proof that the helmets or brake lights make cycling more safe, it only proofs that enough people in power believe in the arguments.
    – Willeke
    Feb 12 at 12:45
  • @Willeke Minor - here it was significantly one woman's drive rather than commercial interests. stuff.co.nz/national/102213259/… Makes for an interesting read.
    – Criggie
    Feb 12 at 18:09

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