I've been testing a dual-LED bicycle headlight that is doing the best-yet job for my (occasionally) very dark commute route. It has 5 output levels (100/200/500/800/1200 lumens (BT30R)) and a separate control pressure switch that attaches to the handgrip and when depressed raises the output to 1800 lumens whether the light is on or off, so it is useful day or night for signaling as well as for inspecting road conditions farther ahead than the normally selected beam.
Riding with this light allows me to select a lower power beam, and then raise the brightness briefly when I need to, which has resulted in much longer battery life as well as being much kinder to oncoming drivers.
The optics in all these lights have fresnel lensing to cut off the upward part of the light pattern that would blind oncoming drivers and bend it down to fill in the dark pool below the main beam and show road hazards directly in front of the bike. The pattern is much safer than most bright bicycle lights with wide beams that put too much light into the oncoming driver's eyes as well as too much light on the ground in close that reflects light back to the rider and reduces his (or her) night vision. I had four LED headlights on my Greyborg when I first mounted one of these, after awhile I found that I didn't need the other lights and removed all but this one.
This light is available in a couple of formats and is part of a family of LED headlights with similar beams, one with a pair of rechargeable lithium 18650's (or four non rechargeable CR123As) that go in the light housing (BC30), the other type is smaller with a separate rechargeable pack that straps to the bike and plugs in (BT30R). This model can be run from an 8V regulated source. The features on these lights vary such as the number and brightness of the levels.
Fenix BT30R, BC30
http://www.amazon.com/Fenix-rechargeabl ... 00VKQQF66/
The BC30R is a dual LED 1600 lumen USB rechargeable model.
Other members of this LED headlight family include single LED versions with similar capability (at 750-800 lumen output) such as the Fenix BTR20. The BT20 is similar but does not have the high beam pushbutton. These single LED lights use the same 7-8.4V remote battery packs, one of which has two removable 18650 cells and the other is a rechargeable lithium pack with a plug in charger. The 18650 removable pack is larger and has a somewhat bulky nylon case to mount it on the bike, I find the smaller rechargeable pack to be a better setup.
I've tested three different models from this family so far (BT20, BTR20, BT30R) and have had good results with all of them, however the pressure switch does significantly improve the useability and power efficiency of the light. I like the capability of changing the 18650's but not the bulk of the nylon pouch for the battery. The smaller rechargeable pack is easier to mount and has a 4 level charge status indicator triggered by a pushbutton on the battery. This pack does require a separate charger which is supplied. Because I can run the light at a lower level and punch it up high when I need to the average power use is lower and the interval between charging can be much longer than other lights which much be run at higher power level all the time.
I buy my Fenix lights from Fenix-Store and Amazon.