When you ride is as important as how many lumens you have.
I found when commuting regularly that I needed a higher output during the dusk period when there is still some ambient light but not enough to see by, 200lm was inadequate during this period and I found 500 to be far better - and this is directed at the road rather than straight ahead. Once the sun has gone completely I found that 200lm was more than adequate to see by even at a decent speed although on off road sections I do enjoy jacking the output up the full 1300lm that my light can output.
I stopped thinking about it once I got a dynamo and lights though - the light I had was the light I had and it was more than good enough.