Candis D.wrote a review of Nite Ize Nite Dawg LED Light-Up Dog Collar on July 23, 2010
It's bright, flashes, waterproof it seems, and as for the sizing complaints, it seems easy enough. My dog is a larger-medium sized dog (50 lbs) and a medium fits her fine. I leave her leather collar on for leashing. This way the light-up collar does not have to be too snug.