A completely dark road or trail out of the city doesn't need as bright a light. Your eyes will adapt, and 450 lumens is enough. You should be able to see okay going 18 mph or less. You can go faster with a light like this, but you might only have enough time to brace for a pothole instead of seeing in time to steer around it.

A "canyon" with no streetlights, and not much traffic? That's no problem.

Some of the most difficult city roads are the ones that are repeatedly bright in some areas and very dark in others. It's harder for my eyes to adapt to the sudden changes in brightness.

And a slight crest in a road with cars coming over the top from the other direction can make it almost impossible to see the road. The road surface isn't lit, and the headlights are in my eyes. I need a strong headlight aimed right in front of my bike to see at all. I can have no idea what's under my wheels--scary.

Wet roads make it even harder to see potholes or debris in time, the surface doesn't reflect the light very well.

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Bike lights are getting brighter. I'd probably prefer 800 or 1000 lumens, to put a bright pool of light on the road in front of me. Then I stand out more with all the car headlights. But I've ridden with 200 lumens in the "old days" and got by.

On a dark country road, 1000 lumens can be too bright--some of the newer street signs and other reflectors are annoyingly bright--they really reflect a lot of light. I would usually click my 1000 lumen light to half power, 500 lumens, unless I was speeding downhill.

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City Canyons
Ha, I first assumed "city canyons" were this:



You could ride with almost no lights here, and still see the road. But I think a bright headlight and good blinky taillight are good for safety. Help the drivers see you.