I did a little research:

According to the

1951 Service Manual on the

Sturmey Archer Heritage web site:

"The output is 6 volts, .34 amps (2 watts) when the cycle reaches a speed of 12 miles per hour"

The 1952 Trade Parts List book lists .3 amp (1.8 watt) and .25 amp (1.5 watt) headlight bulbs to be used with front and rear Dynohubs respectively, in combination with a .04 amp (.24 watt) taillight bulb.

Although I believe the total hub output remained more or less the same, the bulb specifications were later changed. When I bought Dynohub bulbs in the 1970's and 80's the headlight was .2 amps (1.2 watts) and the taillights were .1 amps (.6 watts).

This page from the

1971 Sturmey Archer catalog lists a .2 amp headlight bulb "for large wheel models i.e. 24" and over", a .25 amp headlight bulb "for small wheel models" and a .1 amp taillight bulb.