Ok guys like the title says which is going to give more brightness I see that the 10440 makes the Preon 1 alot brighter will it be the same thing going from 2xcr123 to 1x18650?
It depends on the light's controller electronics. Two CR123s stacked in series will provide appx 7-7.5v nominal, while the 18650 will provide half that. An incandescent bulb driven at the 7v passively supplied by two '123s would burn much hotter and therefore brighter (visually a little more than twice as bright, considering where the blackbody radiation curve of a hotter emitter peaks, and the lesser proportion of total emission occurring in the IR range with a higher filament temperature). However, the LED is not incandescent, and the voltage is not supplied passively to it by the batteries, but rather is actively controlled by the light's electronics. I think that in general, the electronics of lights that are designed to run on either a stack of two '123s or a single 18650 (or multiples of either) will supply about the same power to its LED emitter, and therefore yield the same brightness, with either battery arrangement. This is indeed the case with my JETBeam RRT-3. I just finished a test (posted in a new thread) using a diffusing chamber and a Nikon D700 to measure relative OTF light emission of several lights, including the RRT-3 with six '123s and with three 18650s. The results were identical for both battery sets.
—howard
