My wife and I use Light and Motion. This one.
http://www.bikelights.com/vis360.html It offer great visibility to be seen by cars but needs some additional ambient light. So we use these if we are out and coming home at dusk or for winter riding in the mountains with low light and fog in the daytime. IMO, there is not enough light in total darkness although, we have used them once and it was marginal at slow speed. The other lights they have are much more powerful and provide the necessary brightness for night riding.