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I guess it depends on how much you want to see or if you just want to be seen. For most people riding in cities and towns blinky LEDs will get you seen and street lights are enough to see where you're going. On country lanes you need something mid to high level brightness.
That said lots of cyclists have lights that are far too bright and so many don't seem to understand how to position a front light (IE dipped slightly). Shining huge lights in peoples eyes isn't keeping anyone safe.
Are dynamo lights' output measured in a different way to battery powered lights? All the dynamos seem to be around 200 lumens but the Strada RS is for example is 1200 lumens.
If 200 lumens is enough for riding at night, why buy a 1200 lumen light?