LUX is the measurement of lumens spread over a given area. 1 Lux is the minimum amount of light required to comfortably read a newspaper. We give this reading at 1 Lux as the maximum distance of usable light, anything below that basically becomes inadequate to the human eye.
Measuring with Lux gives the consumer an accurate perception as to how the light will work with the application they are intending to use the light for. Providing the graph gives a visual map of where the hot spots in the beam, how far it will punch down the road and how much flood beam is provided.