Descending at Dusk from White Mountain Research Station, dual Lupine Betty II for 4000 Lumens (video)
Descending at dusk from White Mountain Research Station (12,470' elevation) using two Lupine Betty II lampheads on my Moots Mooto X YBB mountain bike.
UPDATE: I hope to soon take delivery of one or two of the new Lupine Betty 3600 lumen lampheads, which should be even more exciting for this type of night riding.
For high-speed night riding, the Lupine Betty II is like no other light, and more powerful than many car headlights. Two lights are advised for rough terrain when miles from any help, just in case one battery should drain or one light should fail, plus two lights fill in the road so that little concession to speed versus daylight need be made, at least on dirt roads like this.