Don't Look Into the Light
Without fail, it always seems that every time I buy a new light for my bike, I invariably stare into it the first time I turn it on. It happened first with the PB Superflash, and I was amazed with how bright that was. Today I got my Ultrafire C3 Cree Q5 5-Mode LED Flashlight with Extension from Deal Extreme, and again, without fail, I attempted to blind myself.
Fair warning, go with a small sample first, and then if so inclined, slowly increase the exposure. Seeing spots isn't as much fun as the cartoons would have you believe.