Modern LEDs such as a Schmidt Edeluxe run by a generator hub are incredibly bright, and quite sufficient for lighting up pitch-black roads. And they are light enough that it is reasonable to carry a light even when you don't think you'll need one.

Did a short tour along the Danube on the Serbian/Romanian border last year, and didn't figure I would need a light, as I was planning on short days, all in daylight. I brought my Edeluxe anyway, and I was glad I did: the route is punctuated by half-kilometer long, curving highway tunnels with no lighting. Scary enough with the light, but it would have been really dangerous without. And there was no alternate route.