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The MX991\U is a design that has been used by the military since 1940,
is still in use AFAIK. It's light weight, rugged and waterproof.
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They're cheap on EBay, often under $10. One recently went for $3.30.
I modified mine to accept the Maglight 3-watt LED "bulb" that sells
at Wal-Mart for $18. The modification took less than 2 hours, not
counting the trip to Wal-Mart.
It isn't as impressive with the LED as the 2D Maglight with the LED
was, but it's far better than with the stock incandescant bulb and
it's a lot lighter weight and easier to carry than a 2D Maglight. The
Maglight does have a bigger and better reflector so it produces a
better brighter beam with the same light source.
I figure battery life will be about 20 hours of full-brightness
operation. Survivalists might like this because it's military-rugged,
easy to carry, delivers constant full brightness for nearly the entire
life of readily-available cheap batteries (D-cells), and at about
$25 for both flashlight and LED module it's a hell of a lot cheaper
than a lot of LED lights that aren't nearly as good.