Originally Posted by
gear
You'd be surprised at the distance all this takes (about the length of three telephone poles). And that is how far away you should be able to see and identify a tail light as a tail light, if you want it to help you.
The second surprising thing is how many bicyclists judge the brightness of a tail light by standing right behind it (or while holding in their hand), they are all bright at that distance.
That's my way of judging, but I throw in "OK, it's raining heavily at twilight and the driver is texting, glancing at the road for 1 second every 5." And also "OK, I'm heading into the sun at dawn"
Either of those brings me to the conclusion that the light should be visible at about 500 feet in daylight by someone just glancing quickly at the road.
I think I'm gonna go order another one of these lights...