More than 3 watt needed?
And 100 lumens = 1 watt?
To be honest I have never measured a lumen in my life - and I can never remember what a lumen actually is - there's no direct correlation because some LEDs are more efficient than others.
You have to take pretty well all advertised claims with a pinch of salt - shockingly even on Amazon.
If you want a 1 watt torch, buy a "5 watt" one on eBay for £5.
As I said before, B&M do amazing things for £60 or so with only 1 watt / 60 lumens, by using proper optics, but if I was investing, I would want a Philips - but they're over £100 !
I think because I aim my 6 watts per lamp directly at the road, some of it is bounced back and kills my night vision - but my lights really do work - much broader beam pattern. I ride at normal speed on a familiar unlit road every evening.
As I said, I pay £10 for these lamps that are actually about 6 watts.
Doesn't matter which way around you wire them.
12volt 3.7AH radio control battery £25 (knackered after two or 3 winters)
The first year you should be able to get 6 hours run-time on a charge.
Length of twin core, velcro frame bag or water bottle to put the battery in.
Charger £12 - will last for years.
Personally I wouldn't be without one of these now to clamp my lamp to. :-
https://www.google.co.uk/search?q=topeak xtender&hl=en&client=firefox-beta&hs=bEz&tbo=d&rls=org.mozilla:en-GBfficial&tbm=shop&source=lnms&sa=X&ei=_N4LUfGqMtKS0QXlkYGgAQ&ved=0CAwQ_AUoAA&biw=1280&bih=868
Cable tie a plumbing clamp and bob's yer uncle...