Wattage is a poor measure of light output. Even between halogens.
As for a 3 W halogen bulb in a Lumotec or Schmidt headlight
vs a battery-driven halogen headlight, there are a few issues:
– A lower mounting point means that the beam is a bit more useful.
– The Lumotec has a well-designed reflector and the Schmidt E-6 has an even better designed one. You might see beam patterns
here,
here. An E-6 headlight throws light on the road, not in the ditch or in the sky. So all the light is thrown where you need it.
Rechargeable systems typically use an MR-11 spotlight, so most of your beam is wasted.
On the other hand, if you ride in the woods with your E-6, you'll painfully discover its limits because you won't see branches, tight curves...
– Because of their better designs, the Lumotec and Schmidt headlights don't blind oncoming road users.
As for a quick non-scientific comparison (i.e. my eyes), in 2001, I replaced a 2-year-old Vistalite system with a Schmidt hub and Lumotec headlight. The Vistalite system had a 5 W and 10 W MR-11 spotlights. For commuting and on-road riding, the 3 W Lumotec was definitely brighter than the 5 W spotlight, and about as good as the 10 W spotlight. And because the headlight is larger, I find it is more quickly noticed by oncoming drivers (i.e. they don't turn into me).
And this year, I replaced a Lumotec main headlight with a Schmidt E-6 one, and noticed benefits.
As for dual headlights, they are beneficial if you ride fast (more than 20-22 km/h) and in the dark. No need for that if you commute under city lights.