Safety data: Which is safer, head/tail lights which blink or emit a steady beam?

Question

My head and tail lights can be set to blink or emit a steady beam of light.

I usually set my rear (red) light to blink, because I believe it makes me more visible at night. My friend argues that it makes it more difficult for motorists to judge how far away I am.

Are there any studies showing which is the safer way to use a tail light?

Answer 1

The short answer is that 'safer' is subjective and depends on your requirements.

You are both correct. Movement attracts the eye, so your blinking light is noticed. It is easier to judge the position of a steady state light.

For a motorist to pick out your tail light, particularly, from a sea of noise is very difficult. The surface area of the light is tiny, and it's all on its own. Your light is just not important enough to notice amongst the jumble of signs, traffic directions and other cars unless it does something to stand out, like flash.

My understanding is that the reason it's easy to see cars (apart from bulk) is that they have 2 lights moving together. Something to do with your brain automagically resolving the connected pattern. That's why it's hard to see a car with one working taillight, or a motorcycle or bicycle.

In terms of safety, my policy is always 'be seen and misjudged' rather than 'not seen'. So I always set both front and rear lights to blink at night. If you need illumination for the road, I'd strongly suggest a second forward light for that.

From Rear Lighting Configurations for Winter Maintenance Vehicles

Flashing lights will be perceived as having higher brightness than steady-burning lights, up to a flash frequency of about 15 flashes per second. Such brightness enhancement can aid in conspicuity, and several rear lighting systems have been designed to have a flash rate between 5 and 9 flashes per second in order to maximize their perceived brightness. While conspicuity may be greater with such configurations, an observer’s ability to make accurate judgements of relative speed or distance may be compromised when flashing or strobing lights are used. Croft observed that the judgments required in tracking an object were difficult to make under strobing conditions, yet very easy in steady-lighting conditions. Observations made during a study of service vehicle lighting for maintenance operations similarly pointed out that strobing and flashing systems designed for maximum conspicuity can at the same time reduce one's ability to judge relative speed and distance. Periodic sampling of the field of view in another study resulted in deterioration of one's motion-tracking ability that increased as the distance to the object of interest decreased.

Also from Selection and Application of Warning Lights on Roadway Operations Equipment

Flashes are bursts of light which, by definition, are unexpected because they do not occur in nature (save for lightning). This characteristic is their most important feature and why they are so good at capturing attention.

Answer 2

Just a complement to Byron's answer.

Blinking too fast would be counter-productive. For instance, a 20 Hz blinking could get fuzzied, and you would end up with the equivalent of a half-powered steady light.

According to this NASA study (<blink>warning: not about traffic</blink>), the optimal frequency range for catching attention is 4-8 Hz (cycles/second).

NASA also cites "duty cycle", with an example where the light period is longer than the dark period. This increases overall luminosity, and could be a nice trade-off to both catch the attention and allow distance/speed perception.

Answer 3

No data points, but I would agree that in most cases the flashing light is better. A single, constant-burning light can easily get buried in "noise", and there's even a tendency for motorists to unconsciously follow a constantly-burning moving light ahead (especially if drunk), a fact that I suspect figured into a couple of nighttime rear-end collisions I've learned of over the years.

To improve the ability of the motorist to judge the location and speed of the light it's better if it flashes relatively rapidly -- maybe 2-3 times per second.

Re legality, 169.222 subdivision 6 of the Minnesota statutes states:

A bicycle may be equipped with a rear lamp that emits a red flashing signal.

Answer 4

As a driver, I would recommend flashing LEDs front and back since it warns me that a cyclist is there. Unfortunately, even motor bikes with their much better lights can disappear into the mess of other lights.

Answer 5

A blinking light is disturbing, even after you have been noticed, even from the opposite direction, it is hard to concentrate on something else. In Germany, these blinking lights are prohibited, and right so. Stop using them!

Maybe you are safer, but the rest of the traffic is more unsafe. If everybody starts blinking and flashing, driving will become impossible.