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Today, the newest choice is the same form factor but with “LED”:http://www.lightmanstrobes.com/ledlight.htm flashers. The main advantage is that with two AAs, the Xenon might last 2 hours, wheresas the LED will alst 50 hours.
As a backup, the new el cheapo LED lights are not a bad choice. For instance, the Cat Eye “EL400”:http://webcyclery.com/product.php?productid=16774&cat=346&page=1 is just $34 has 3 white LEDs and with three AAAs, lasts 160 hours!