I ride a little over 10 miles to work. It takes 35 to 50 min depending on the wind and how I hit the
lights. The purpose of the light is primarily to be seen since most of the route is lighted with
streetlights.
The best solution I have come up with is to use a 13 watt emergency lighting sealed flood powered by
an electric drill battery (all available at Home Depot). The flood is about 4.5" in dia, all plastic
(light), and throws enough light to see obstructions at 20+ mph (it throws a bright horizontal bar
with a wide flood). More importantly, it's big enough so motorists (so far) have not ignored it.
It's glued with gloop to a formed hunk of aluminum strap. The aluminum strap is velcroed to the
helmet (only need the thing during spring & fall).
I found that I could buy a 12 volt rechargeable drill cheaper than I could buy a battery and
charger. The charger is fairly light, so I carry that too if I need to run the light on the way
home. The battery can run the light for a little over an hour and the charger can charge it within 8
hours. A hunk of light cord with a wheel switch is all that is required. I just rubber band the cord
to the battery.
The total cost was in the $50 range including the drill.