The first digital watch I ever saw was on someone else's arm in a crowd, during a trip with my parents to Seattle sometime in the mid-1970s. Unlike every digital watch manufactured today, it used light-emitting diodes (LEDs) instead of a liquid crystal display (LCD), and the owner had to push a button to get it to light up and tell the time -- to save on batteries. In 1974, my dad also bought one of the first full-featured scientific calculators, a brick from Texas Instruments that also used LEDs and had a big power adapter to plug into the wall when you weren't using a 9 V battery to power it. I think it cost about $225 at the time.
Sure, LEDs are still common for the displays on stereo components and as blinkie lights on modems, but you might think they're passé for anything else. Yet they are swiftly coming up as a possible replacement for traditional incandescent and fluorescent light bulbs. The first to appear widely in public are as traffic signals and taillights on buses and trucks, because they last longer than old-style incandescent bulbs. Now you can buy LED flashlights (including a very cool model that needs no batteries -- you just shake it), and household lighting isn't too far away.