[martijnvds]

In the Netherlands, bike lights _must not_ flash. The law very explicitly states that they need to be "always on" (in the dark).

The main reason seems to be that it's hard for others to to gauge your speed when your lights are flashing.

[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.

[arccy]

but also there are so many bikes there already that they didn't need to raise general awareness that much