Massive 4"+ Sturmey Archer lamp

This gigantic old lamp was acquired on ebay. It has provision inside for two batteries as well as two exterior terminals for wiring to a dynohub, a 3 position switch on top & both dim & high beam bulbs.

 

At the top of the chrome shroud is a large brass badge which reads 'Sturmey Archer Dynohub Patents pending', Although this has proved impossible to photograph!

Does anyone have any rough idea how old this lamp might be?

 

EDIT: Early 1930's.

Done