terrymorse 

Which type of rear bike light is safer, a steady light or a flashing light?

Somebody did the experiment. A preprint:

Bishop et al, The effect of rear bicycle light configurations on drivers' perception of cyclists' presence and proximity, 2023

Edit: Full text of the article.

Experiment 1: Detect cyclist as quickly as possible.
Result: No difference [detected] between steady and flashing.

Experiment 2: Estimate distance to cyclist.
Result: Flashing light more accurate than steady light.

I've been using a flashing rear light during daylight, and it seems that's the safer choice.

tomato coupe

They should have included lights like the Varia that change their mode/pattern when they detect an approaching vehicle.

cb400bill

Flash during the day.

Solid in the night.

theblackbullet

The only time I've ever used the steady mode on my tail light is when I'm riding in a group after dark. Flashing mode almost always otherwise.

Rick_D

Good to see somebody investigating this, since it's not terribly clear to the user which might be better.

Light and Motion has committed to pulsing, rather than flashing beacons. My recollection is they're less dazzling to drivers while still attracting more notice than steady state. Can attest when driving, some strobing bike headlights are pretty hard on the eyes, perhaps affecting perception of distance to the bike itself.

Any kind is better than none, at least when there's traffic!

terrymorse 

They did. No difference was detected between steady flash and "adaptive flash". At least no difference was reported in the abstract (full article not yet published).

shelbyfv

Traditional cycling etiquette is steady mode when riding with a group. Flashing does seem more visible when riding solo. I've been impressed with how much more visible approaching cyclists are when they are using a flashing white front light.

easyupbug 

I watch carefully
for cyclist lights and firmly believe I distinguish a flashing or some of the adaptive flashes even quicker as a cyclist rather than a car/truck/motorcycle. Only reason maybe because some of the flashing lights I have seen are reminiscent of an auto/truck/motorcycle turn signal.

Koyote

The next experiment will hopefully involve multiple lights -- perhaps one flasher, one steady, mounted as far apart as possible (one on seatpost or even helmet, one low on seatstay).

Maelochs

I haven't seen the methodology but I believe similar tests have been done .... and like @easyupbug I pay attention myself. I find solid lights are more easily confused with roadside markers or reflectors. Flashing is associated with motion in the human brain, which is sort of hardwired to a response .... as far as I know.

No doubt it is far easier to estimate closing rate with s solid light, but I don't care ... the sooner someone notices me the sooner that person will begin planning not to hit me.

Sy Reene

Syncopation

Eyes Roll

A safety-colored vest or jacket with reflective material enhances your visibility and is generally safer than bike lights, both during the day and at night. My preference of color is safety yellow. A blinking red tail light definitely draws the attention of car drivers passing from behind and from a far-off distance at night, but may not be enough during the day and a safety colored vest or jacket provides much better visibility. A vest or jacket is bigger than a bike light, so, it provides greater visibility.

I never ride my bikes without a safety yellow vest, helmet, and gloves on.

rsbob 

I understand your preference for a vest but what data do you have which supports your assertion that a vest provides better visibility than a high intensity flashing light?

there are lots of low intensity lights but there are some which can be seen a mile away in bright sun. I don’t begrudge your fondness for a yellow vest but high-visibility yellow-green have been demonstrated to be more visible.

Eyes Roll

Your brightest bike tail light that can be seen from a mile away may run out of battery/charge behind your back and turn off without your knowledge, but a safety colored vest will always have your back, providing visibility and safety. You make your call.

LesterOfPuppets

I glance down and see my seatpost mounted light reflecting off my chainstays and cassette. I'll know if it fails within minutes. Back when I had a 60-75 minute night commute, I'd bring two rear blinkies JIC.

Definitely wouldn't trade a rear light for a vest but I could see going for the belt and suspenders approach.

znomit

All those vests are invisible to a car with dipped beams. Most clothing friendly reflective material tends to work poorly in the wet too.

PeteHski

A Garmin Varia battery lasts about 10 hours in daylight flash mode (which is seriously bright) and the head unit warms you when the battery is going flat, so that is not an issue.

I rode a sportive event a couple of years ago and at the end another cyclist came up to me and commented how he had been using my flashing tail light as a beacon to chase down when he was over half a mile behind on the road. This was in broad daylight.

PeteHski

I prefer to use a flashing rear light (Garmin Varia). As a motorist I have observed that I pay instant attention to flashing lights as they are associated with a hazard or emergency. I may not see a flashing light any earlier, but I will pay more attention to it than a steady light. Turn indicators are flashing to attract your attention. If they were steady lights then you probably wouldn’t notice them.

Most UK cyclists use flashing rear lights for the same reason I do. A relatively slow moving cyclist in traffic is basically a road hazard. In the UK, motorists will often put on their flashing hazard warning lights if they are slowing down approaching a traffic jam to warn following drivers to slow. Or if they are driving very slowly for some other reason. A bicycle with a flashing rear light conveys the same message ie hey be careful I’m a slow moving hazard!

Maelochs

Here is another issue ... if the driver isn't looking ....

Also in the photos above the yellow vest stands out ... but all the cyclists are visible. If the driver is paying attention, s/he will see what's ahead. Whether or not I have lights, the car has some pretty bright lights .... if the driver is paying attention .....

During the day I am not worrying about being more visible than everything else on the road ... and since I have been riding mostly safely for all these decades I have to assume a hi-viz vest is not a huge benefit during the day. At night I prefer to wear brighter clothing because a car's headlights might only cross over me for a short time ... but really, the question is also one of contrast. if I am dressed all in white on a white bike riding along a white fence then even if the headlights pass over me .....

Anyway, if high-viz were the answer, no one wearing high-viz would get hit and people not wearing high-viz would get hit .... which seems not to be the case.

I have also been riding at night and had my light fail (particularly back when bike lights were pretty lame) and yet ... I am still here. . I have even spotted ninja cyclists at night outside of the range of my lights just because there are subtle flickerings in the dark. Our eyes can do that ... it is one of the reasons why we weren't all eaten back when people got eaten.

In any case, tests seem to have shown that the type of lighting which is most immediately recognized by drivers as "Bicycle!" is a pedal-mounted light, or an ankle light. Apparently nothing else on the road has the same light signature as an ankle or pedal light. Yet, we put all our technological wizardry into tail lights. Surely we could develop a pedal light or a shoe light or something which would be very light, very small, and easily rechargeable ... but no one wants one.

Whatever ... when cyclists get his, it isn't always because they weren't using lights or hi-viz. Last breakdown I saw, a few years back, was that a huge number of cyclists who ended up in the hospital were salmoning and/or riding without lights at night ... so not only were they not seen but they were coming from unexpected directions .... but there was no correlation with brighter lights or high-viz. Also, alcohol use by either or both driver and rider correlated high.

Which is the main point: You can wear whatever, and a bad driver will hit you. Just last week a lady in Gulf Stream, Florida plowed into a bunch of cyclists, all using lights and some wearing high-viz, killing one and hospitalizing six others. A coupe years ago, a lady in Davie, Florida, plowed into a bout two dozen riders because she was looking for condiments for her fast food burger ... two died.

Lights are an aid, hi-viz probably never hurts, but luck and awareness are what we really need. And since we cannot control our fates .... I just accept that even if I wear high-viz and use two, flashing out-of-synch tail lights and a solid light, and an ankle light, some idiot might run me over from behind. Until I see one headlight beam on each side of me, I won't know ..... but it is more likely that I will fall in the shower and crack my head on the faucet.

That is why I wear high-viz in the shower.

PeteHski

I think where all the viz and flashing lights help are when motorists are looking, but not really paying much attention. The more you stand out, the more likely it is that you will draw their attention.

Motorists tend to focus on the biggest and most threatening objects in their field of view, such as large trucks, buses and other cars. Cyclists are both small and non-threatening. Flashing lights just help to address that inherent disadvantage by triggering the motorists’ hazard warning instinct.

But if they are not looking at all then there Is nothing you can do. Just have to hope the truck hits them before they hit you!

Maelochs

The next big cycling safety device will be a compact but ridiculously powerful 5G transmitter so cyclists show up on the cell phones of all drivers withing a quarter-mile radius.

eduskator

Flashing. It's an eye catcher. You want to draw as much attention as possible.

It doesn't make a difference? I would like to see / read more research on this.

datlas 

Realize this study was based on people watching films/videos of cyclists and not drivers looking at actual cyclists.

That would be a better study but more complicated/expensive to do, so I am not holding my breath on that one.

eduskator

Yes. Hence why I would like to see more research on this. I read the summary and I'm not convinced that this is a strong or very credible study.

Seems like a no brainer to me that flashing lights are seen quicker by the human brains than steady lights. However, I could be biased.

datlas 

I suspect you are correct. I also suspect that a film/video does NOT capture the "alarm" and brightness of a flashing light due to various reasons including S/N ratio, FPS and other technical reasons I have no understanding of.

So the study has limitations.

A real world study would be much more useful, but as above I am not holding my breath on it.