Originally Posted by JohnJ80

Car headlights are 700 lumens on low and 1200 lumens on high (halogen, LED are much brighter) - on that you're wrong.
100 lumen tail lights and 500 lumen head lights are not going to be blinding anyone much less during the day. At 100 lumens, we have more than ample safety overhead. In point of fact, we're approaching almost an order of magnitude of difference. With a 500 lumen headlight on a bike, we aren't even near what a single car headlight puts out.

At 4m, if I blind someone with my wimpy and almost useless 40 lumen taillight, I have other far larger problems. Besides that, lux - the amount of lumens square area decreases as the square of the distance away from the light source. So if I go to 8m, the effect is 1/4th as strong. But other than that, go take a 40 lumen light out on a 45 mph road and see how far away it's useful. The vast majority of them are almost inconsequential at 500' (about 6-7 seconds of warning for a motorist at 45mph). Granted, better optics help a lot and really help a lower lumen light punch above it's weight for sure.

You can add to the visibility of the light by flashing or pulsing - on that agree and it also agrees with the research that Bontrager relied upon for the flashing interrupter patterns their Flare series of lights use.