Cycling in Sydney Australia
Lux: a measurement of light taking area into account.
Lumens: total amount of light emitted from a source.
A 1000 lumen light source over directed over 1msq is 1000lux.
A 1000 lumen light source over 10msq is 100lux.
lux (with almost all bike lights) measured on the ground falls off with distance as the light spreads.
As a photographer using artifical lighting you understand light fall-off, the inverse square law, feathering.