Originally Posted by
lostarchitect
I think the most important thing is that it flashes obnoxiously.
I agree with this when the objective is to be seen.
For taillights, I've got a flea on the roadbike, nightrider cherrybomb on the utility bike and a Blackburn Mars 3 on the tandem. I don't like the flea much, for reasons other than the on-bike operation, which is fine.
For headlights I have a cygolight 200 lumen and a Nightrider 150. Both have an obnoxious flash mode. I have a 150 lumen flashlight that I can put where needed, but it doesn't flash. I consider 150 lumens the minimum for seeing by. For "be seen" duty, lesser power is ok, but obnoxious flashing is a must.