The TerraLux bulb above will fit many flashlights with standard bulb fittings and it has a wide voltage range.  BTW, it comes with the voltage circuitry inside.  The first gen LED I bought for a Maglite was a simple LED without the voltage reg circuitry.  The one above is much better IMO.
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Better is the Enemy of Good Enough.  
Okay, what’s your point??