[crazygringo]

Fascinating. I just looked up a bit of research on it, and it seems there are two contradicting phenomena at play. Flashing helps in seeing cyclists further away and helps with visibility generally -- but it also makes it harder to estimate speed and distance.

Apparently, the absolute safest solution is to have two rear lights side-by-side -- one that is always on and one that is always flashing.

It doesn't seem like there's clear data on which is safer if you have to pick only one. Different countries/states have chosen differently.

[exmadscientist]

Flashing on-off and always on aren't the only options. I wish more designers went with flashing bright-dim, because it solves a lot of problems.

I once worked on a device where we were required to blink the Important Safety Light™ on-off. I often glanced at this light out of the corner of my eye, and saw that it was off, so we were Safe™. We were not Safe™: it was just in the off phase of its blink.

I am very glad I never got hurt by trusting that light.

I wanted to blink it bright-dim but was denied by people who said that IEC 61010 required it to blink, and blinking bright-dim isn't blinking. I didn't quite understand that objection.

[crazygringo]

Having a third brightness state feels confusing.

If a safety indicator needs to be visible at a glance, why did it blink at all?

Blinking only works for things that are in your vision and need to be the primary focus.

It seems like blinking to begin with is terrible design for something like this, or else having it be in the corner of your eye is the terrible design decision.

[exmadscientist]

> If a safety indicator needs to be visible at a glance, why did it blink at all?

Beats me! But they've apparently flashed for ages and ages on these things, and somewhere along the line it got standardized.

> It seems like blinking to begin with is terrible design for something like this, or else having it be in the corner of your eye is the terrible design decision.

This is benchtop equipment, not cars, so "corner of your eye" has a little bit different context here. But, yes, I kind of agree.

It is also really important to get this one right since for this particular type of device, conditions are lethal (yes, genuinely lethal, no exaggeration) if you get cavalier with it.

[Y_Y]

This is a strong point. Nobody likes a rapidly flashing light (extra annoying, seems broken, can be hard to differentiate from "on but dim"). Then again if you flash slowly then you'll have some appreiable amount of time when it's off and that can include the entire opportunity you have to look at something.

Ideally (for me) you could have smooth high-low alternation or colour alternation.

(I recognize that something that looks like emergency services, e.g. alternating blue/white may be illegal, and that colour-blindness may limit this approach.)