"Usually", when they don't mention lumens, the lights are cheap and not very bright. Lumens are supposed to be the total light given off. Lux is light per area, so a very narrow beam could have larger lux than a very bright light that is spread over a wide beam.

The MTBR Lights Shootout measures lights with their own lux meter, and they are attempting to use the same measurement of total light output on all their lights, so they can be compared to each other. Some manufacturers are pretty accurate in their lumens, and other exaggerate a lot.

But each doubling of lumens only makes the light look "a little" brighter. So, for instance, the difference between 450 lumens and 600 lumens isn't real big.

I would look for 500-600 lumens to light up the road at normal road bike speeds. I have 1100 lumens that are great in the city, lighting a big pool of light on the road and competing with car headlights. But it's often too bright on very dark country roads, so I run it on medium, about 500-600 lumens. ( You can always run a light on medium or low, so it's good to have lots of lumens--for downhills or competing with car headlights in the city)

When I was looking at the lights reviews, I paid a lot of attention to the beam spread. Some lights, especially flashlights, have a central bright spot, with a surrounding dimmer area that cuts off suddenly at the edge. I like a beam that gradually tapers off at the edges, with no bright spots or dark lines showing.

( I used to use a 200 lumen light and it wasn't quite bright enough to go 18-20 mph and see potholes in time)