Watt rating is one of the least useful as it's the power input to a light, not the light output. For example, a 1W incandescent bulb would be useless as a bike light whereas a 1W LED could provide a useful, albeit rather low, amount of light because LEDs are much more efficient than incandescent lamps.

Lumens is a measure of total visible light output. Accuracy and truthfulness of measurements vary. How that light is distributed is also important. Lux is a measure of the maximum brightness in a beam (Lumens per square meter). For a given Lumen output, a more tightly focused beam provides higher Lux. Taken together, Lux and Lumens give a descent idea of how a light might perform, but they still only convey the total light output and the brightness at the center of the spot, not how the light is distributed around the center of the beam.