On the topic of LED bulbs in 2 cell Mags, the EverLED in a 2 cell Mag is the biggest improvement of output! Using the EverLED in a 3 cell light, there is a huge improvement in color and beam quality, but not really in output in my opinioni. On the other hand, comnparing the EverLED to a Krypton or Xenon bulb in a 2C or 2D Mag will make a believer out of ANYONE!
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Regarding the Minimag options, I've never owned any of the Luxeon sandwiches but have tried the Opalec and countless numbers of single LEDs that I've just run direct drive. Many 3mm LEDs you can use as is after cutting the leads to correct length. To use 5mm LEDs, you will need to drill out the reflector a bit but this is easy enough. Incredible increases in runtime can be achieved going this route. I have a Minimag knockoff (with a stock clickie!) that has a 3mm green LED that achieves full brightness at 3V that has got at least 20 minutes a night and is still on the first set of alkalines which have been in for 2 months and are still going strong and the new 26,000 mcd LEDs are very white and get very bright on 2 cells of any kind, esp lithiums.