The lower the light is to the road surface the brighter it will appear.
I first got the B&M Lyt BN that Brompton was Using , its 15 'Lux' ( lumens or lux you figure out the conversion difference , if it Matters)
http://www.bumm.de/produkte/dynamo-s...motec-lyt.html
It had a 2nd input to be fast to fit at the factory ..
Mine was from a dealer, not from the factory.. Narrow spot was Bright enough at 19" off the pavement
but lacked standlight, so I returned it and Got an Eyc-T instead
all models have standlight and the beam spread is wider..
http://www.bumm.de/produkte/dynamo-s...c-iq2-eyc.html