Posted by Deliverator on September 7th, 2006
I recently added another LED flashlight to my growing collection, a “10w” model sold by Fifth Unit. Fifth Unit operates very similarly to the now defunct AXShop (namely, obscenely low prices and long ship times), carrying much the same type of wares and is rumored to have some of the same employees. This new flashlight is much the same as the “7w Golston” I also own, with a virtually identical casing and a slightly different, recessed, two brightness mode end cap. The main difference is the use of the new Luxeon K2 emitter. These new emitters put out more light, can have higher driving currents and tolerate higher operating temperatures than previous Luxeon LEDs, which were still industry leaders in brightness. In reality, despite the 10w vs 7w designator in the name, this new flashlight is only nominally brighter than my 7w and actually has a slightly weaker “throw.” The real reason I was interested in this new flashlight is that it is capable of using the higher voltage lithium ion CR123 rechargeables.
There are basically two versions of a Lithium-ION CR123 rechargeable. One is designed as a drop in replacement for disposeable 3v Lithium batteries. A good deal of the interior space of these 3v Lithium-ION is devoted to regulation circuitry and devices to keep the cell from exploding or doing other nasty things due to deep discharge, overcharging, overheating, etc. As such, these cells have a much lower amp-hour rating than a disposeable cell. Even with the lower amp-hour rating, these rechargeable cells are often not very useful in flashlights without a voltage regulator circuit. When loaded, the voltage output by these cells quickly drops below a useful level and the LED flashlight quickly dims. So, even though these cells still have a lot of juice in them, they don’t produce enough forward voltage to get the LED to light up very brightly. When I use 3v rechargeables in my 7w Golston flashlight, I get maybe 15 minutes of bright light out of it, if I use it only intermittently. If I leave the flashlight on continuously, I get even less useful life out of the batteries. Thankfully, there is a solution. There is another type of lithium ion rechargeable CR123 cell available. These don’t waste a lot of space to regulation and as such have a higher amp-hour rating. These cells also have a much higher voltage, usually about 3.6-3.7 volts loaded. Hot off the charger, these batteries will be as high as ~4.2, which is high enough that you can burn out some devices designed for 3v disposeable CR123s. 4.2 volt cells are too much for my 7w Golston with its already overdriven emitter, but these cells work quite well in my new K2 based flashlight. In addition to the greater AH capacity, these cells stay above the needed forward voltage bias needed to drive the emitter at peak brightness for a much longer time.
This summer, I have taken to walking around the hill late at night listening to Podcasts. With my 7w Golston flashlight running off 3v rechargeables, I had to use my flashlight intermittently or risk running out of juice before finishing my walk. With my K2 flashlight running on 3.7v rechargeables, I can leave my flashlight on for the whole hour without worry. There is great peace of mind in not having to worry about quickly turning on your flashlight just so that the drunken guy in the beat up pickup truck (who hasn’t yet quite figured out the headlight switch) doesn’t run you over.