If I know my route and it is general well-lit I use about 250 lumens. More as needed.

I have two headlights, Light and Motion Urbans, a 500 and a 750. For battery life I run low lighting when I can but I have the option of going full blinding if I want. On an completely unlit and often tree-tunneled MUP I use both lights, one long and one close---I can afford to because no one uses it at night. if I am going quickly (relatively) I use more light---because each light can be aimed independently, I never need to blind drivers to be able to see the road adequately. If I am an unknown road where anything could show up .... etc.

Like [MENTION=458715]55murray[/MENTION] and [MENTION=388062]kingston[/MENTION] I find that “bright as day” lighting is generally overkill. For one thing, the brighter the lit patch, the darker the rest of the world. Soe like that, some don’t. If I were riding off-road, I would definitely go with [MENTION=454965]Kapusta[/MENTION]’s massive overkill solution … but for most night ridesI just need to see obstacles in time to take sensible action.

Tail lights, max brightness, because I don’t ride in a peloton often.