My experience with led
's, dating back to the 1970's an 80's, is that they have an approximate life of 100,00 to 300,000 hours depending on the color. The blues have only been around for the past few years and reds and greens have been around for decades. They draw infitesimal amounts of current and produce incredible lumens/per watt. Many cities are replacing their traffic light bulbs with led
's as well as automakers and dozens of other industries. They are simply cheaper and more reliable than other types of lighting.
As far as spectrum and how they help/hurt a reef tank, I dunno. But they are cool.