About 11 years ago when I got serious about commuting to work by bicycle year round I had to tackle the challenge of riding in the dark, as the sun sets around 4:30 in winter. At that time there were expensive external battery systems with halogen lights for serious riders, but I opted for lights with built in batteries. By today’s standards they were pretty dim, and I had to ride fairly slowly on streets with inadequate street lights.
It was a tremendous breakthrough when I got my first LED light with rechargeable Lithium Ion battery a few years later. It was rated at 200 or 300 lumen brightness and could run three or four hours on a charge. And I could charge it via USB with a wall adapter, or even on my computer at work.
A couple of years ago I upgraded to a 600 lumen light, which was amazing to me. Today you can buy a 1000 lumen light for under $100. LED light technology has really changed the game, with dramatically increased brightness, while using much less electric power, making them perfect for battery operated bicycle lights.
I have two objectives for my headlight solution–bright enough to see the road well in front of me, and attention grabbing so cars will see me. For the second objective I opt for a flashing light. And I even use the flashing light during daylight hours, too, to increase my visibility to cars.
I add a red blinking taillight to increase my visibility to the rear. Usually two of them, in case one malfunctions or runs out of battery, and just to increase visibility.
My new commute bike introduced me to a new light technology. Paired with the LED front and rear lights, it uses a dynamo front hub to power the lights, instead of batteries. I found the front light which came on the bike not bright and focussed enough to light the road as well as my battery light, so I purchased a better one. This new dynamo powered front light is my main headlight, and I supplement it with a battery light which I run in flashing mode for visibility. It is convenient and safer to have these front and rear lights always ready to operate, without worrying about the charging state of the battery.
Here is a great website for researching bike headlights, especially dynamo powered ones.
http://www.peterwhitecycles.com/headlights.php