Switch is on light head in front.
Hey two 18650's! They must have been reading this forum! They were cheap; I need to save my money to buy more fasttech panasonic 3400's; so, I bought two. It was easy to unscrew the battery compartment and glue/solder inline a variable resistor (25 ohm 3 watt rheostat from Radio shack $3.95 or so.) Now I can get any drive level I wish, down to 12 milliamps. My added dimmer, though, is on rear--which is fine with me.
My first thought on first one was that, while the xml head is bigger, this was easily offset by the forehead plastic supporting piece. As the fourth bike xml headlamp for me, this one was extremely comfortable to wear--unlike the other first three brands of xml headlamps.
They seem to average about 1.6 amps on high (using heavy gauge test leads, and 4.19 volt off charger. 1.9 amp is the highest I have measured) and 300 or 350 milliamps (don't recall) pwm on low--with new cells (but as voltage drops, so does output/current, making the rheostat work fine). So for me, too high on high, and too low on low.
All in all, it seems to me the go to light for most tasks, for compact size and output. Not quite as good on colors as the hp11, nor throwy (about 3/5 throw per watt), but with the battery format, we now can afford more current in one day of usage.
They don't spec out ar glass, but I don't see much loss there. (the lens screws off for pure flood. But comparing to hp25, same lux at same current, just half the lumens make it out the head.)
The second one I bought, has bigger hotspot than first (same lux in center-just less uniform center; same lux in corona) and on the second light, they skimped on elastic-making wearing it for about 50 needed to stretch it out before it didn't feel too tight.
Obviously, don't buy it for wet use. Don't use unprotected or no-name brand cells. It surprisingly uses silicone to protect head from any possible flames. (Silicone is a good insulator and melts at 2400 degrees F. )
I get about 5350 lux,\-err., I mean candela- at 700 milliamps to led. (The hp11 would get 7800, the hp25 is 5700 candela at 600 + milliamps). So, compared to hp25 on high, the hp25 feels like you have tunnel vision, with about same fovia stimulation. (The hp25 flood is great, but not good for more than a few feet.) Comparing with hp11 on 9 hour (130 lumen) you only feel like this is about a %25 improvement (but using more than double the juice). Comparing with hp11 on turbo, the hp11 feels much brighter, but approximately same output to this light in lumen terms. Naturally, I am limiting at 700 milliamps for 8+hours of use off two 18650s. You can get over 10k candela by opening resistor wide open-with short runtime. Again, color rendering is okay-nearly the best of any of my xml lights-, but worse than the Fenix BT20's t6, and worse than any of my xpg's. The led star says U2 on it on both lights, but I do not know if this is just something they print on all cree stars, or if this is a switcheroo. I don't care too much as the led demonstrates competant output and color rendering-housed in a good reflector/heatsinked/glass lens setup.
The wires to head seem thin, but do have the curly flexible shape. The led is house so that it would be easy to replace when something better comes around.
Were I camper on biker, regularly relying on this light, I would heavily modify to make it rain resistant. And carry special bag and cheap waterproof alternative for deluge times. The driver in the non water proof batter compartment will short easily and burn out, so only touch the pole going to charger when adding a rheostat.
I would stay away from the other sku of this light for $27 that comes with batteries and charger. Since these 18650 are really only 700 milliamp-hour and I wouldn't trust the charger.
Beware, the kaidomain 3 t6 xml headlamp that claims 2000+lumens is dimmer than this light--and far worse color rendering. (I couldn't help myself on three xml headlamp.) Dx.com had a single 18650 xpg dual flood + throw, that turned out to be a rip off (burned out in 10 minutes of use), not even an xpg at all (xpe) and flood was a 50 lpw purple, overdriven zongshen led. My other dx xml u2 bike light has much worse color rendering than this one, and batteries that come with it are junk.
Also, if you modify your non constant current contoller by adding a dimmer (to better control runtime), I would recommend using your amp meter to train yourself how to dim (how a fraction of a tweak can lower current). For ex., a slight tweak can drastically lower current; so, two slight pressure tweaks and slight dimming will half the current to 700 m.a. from 1.6. While this will make one miss the constant current driver for better control, this method is probably better subjective control for putting out as much light as one needs. My emotional connection is still with a constant current driver. However, to my lux meter and eye, this light's controller + var. resistor is more efficient than the 700 ma buckpuck. A constant 700 ma is idiot proof, though.
