Originally Posted by
buzzbee
Lux is lumens per sq meter (so where do you position that square meter).
And light falls off with distance. What is not quantified is the shape of the emitted beam.
All of these, including the shape of the beam and intensities in different directions is quantified by German law
http://swhs.home.xs4all.nl/fiets/tes.../index_en.html
Some of it doesn't translate so well into English, but this guy gives it a shot and does complain that it's not precise enough.