Halcyon uses LUX to describe diving lights because this provides a gauge of intensity at a given distance. This gauge is more relevant for use while diving and specifically for signaling your buddy while diving.
Halcyon typically tests lux output at one, three, and five meters (about 3, 10, and 16 feet respectively) from the light. These distances are useful when comparing dive light intensity.
It’s worth noting; a lux measurement that is taken very close to the light source will be higher than a lux measurement taken at a farther distance from the same light source. This is because the light diffuses as it gets farther from the source. Given this, you can think of lumens as the amount of light available and lux as the lumens that are actually arriving at the target.
Watch more on Lux Vs. Lumen on the video below