Koga OEM B&M 4D toplight, Rack is a Tubus, so that was easy.
Rack like Igo's would take one too.
an EU standard type mount , these days.
Use the 2 holes Horizontal, 50 or 60 mm apart, instead of vertical and 20mm apart.

Bike came with a battery one, got a Multi to run off the Hub Dynamo.

Got kludgy, and made a way to mount the other one
down by the water-bottle cage, on my rear rackless B.F. P.Llama..
Low , so my rain cape wont hide it.