Ahh...finally somebody who is talking something really useful. That is right, 1 lux at the target. It is also quite easy. Eg, 400k lux light @ 1m, throw = sq rt of that = 632m. Easy.
Searchlights... Check out the PDFs...play with the lux and PBCP with the above formula.
http://www.francis.co.uk/technical.asp
You can easily see past 400m, even past 8km (I just done that last week somewhat). My country has pretty high humidity 90% of the time. The fact that you are not seeing stuff past 200m, 400m for LEDs is simply they are not powerful enough, just that and nothing more. I now have 3 lights which go past 1 million lux @ 1m and another stuck at 800k. (actually my DX sort of under reads by about 10-20% compared to the good ones)
PS, I am not dissing lights like SR90, TK70, DEFT or even customs with 250k CP. My TK70 copy is due to arrive next week from Hong Kong.