I purchased a new bike headlight last year but have not tested it much until this last week. It did a better job for me than the other lights I've been running. Here's the full report:
Tonite a meeting ran late so I had the opportunity to test my lights after dark.
My commute is about six miles on a twisty 25mph road through a park, and another six is along a 50mph highway on a mostly-wide bike lane separated from the traffic by a solid white line. These areas are totally unlit and the pavement through the park is chip and seal which is rough and needs a careful eye. The pavement along the highway is relatively new but there are rough sections and many hazards littering the route, from glass and gravel to trash, lumber and occasionally raccoon and deer bodies which are hard to see with their light absorbing fur.
The Fenix BT20 is a light that I bought earlier but have not used much. It is one of the few bike lights I've seen that makes an effort to produce a pattern of illumination that matches the needs of a bicycle. It does a pretty good job. Better than the other 3 lights I've used - the Cycle Lumenator and the 1000 lumen MagicShine 808E(w/ and w/o spreader lens). The MagicShine with a spreader lens is actually the second best, the stock MagicShine is third and the Cycle Lumenator is last when it comes to putting a good pattern down 30 yards out.
The Cycle Lumenator runs directly from the ebike battery and puts out a lot of light in a large flood pattern which is convenient and excellent for some things, but not quite what I need running in a bike lane along a dark highway. This is similar to many other multi-LED lights that put out a lot of light in a wide beam. Drivers flash me when I run this light, even tipped down. They think it is too bright into their eyes. It doesn't put much light out at a distance (since it doesn't have much of a hotspot), but it does light up in close very well, whether downward on the pavement or upward into the trees and overhead wires.
The stock MagicShine makes a reasonable "high beam" but it puts too much light in the eyes of the oncoming traffic (and drivers don't like it - they flash me). Adding the spreader lens really helps a lot in terms of a nice pattern, spreading it out horizontally and reducing the beam upward as well as blocking driver's direct view of the bright LED die.
The Fenix BT20 750 Lumen Dual Distance Beam has a fairly bright large spot for distance, a fairly dark upper area to protect driver's eyes, and some light kicking down lower in front of the front tire to view the road surface in close. It has four power settings plus strobe and works with either a pair of 18650 rechargeable lithium batteries, or four CR123A primary lithium batteries. They use various tricks to shape the beam including stippling the reflector and adding fresnel refractors to the lens.
The battery case is a bit of a pain to work with, it has an O ring and a removable top held with a thumbscrew. The two rechargeable laptop cell 18650's should run about three 45 minute commutes in high beam (according to specs). There is a coaxial jack between the battery and light so it should be easy to power this from another 8 volt source such as a DC-DC converter. It might work from 12 volts WARNING THIS IS NOT TESTED OR ADVISED BY ME.
The BT-20 is available from many sources, including Fenix-Store and Amazon.