Example of SON Edelux II Dynamo Headlight mounted below an Ortlieb Ultimate 6 Plus. 

ALL parts used: 

Ortlieb Ultimate 6 Plus Handlebar Bag- 8.5 Liter 
Ortlieb Part #
F3252

Ortlieb Mounting Set For Ultimate 6
Ortlieb Part #E815


Ortlieb Ultimate Bar Bag Adapter for Lights, GPS ect
Ortlieb Part #F1451


SON Headlight Bracket for Delux - Long - Milled - 31.8 mm Clamp
SON Part #75534