NEW YORK - The light bulb, the symbol of bright ideas, doesn't look like such a great idea anymore, as lawmakers in the U.S. and abroad are talking about banning the century-old technology because of its contribution to global warming. But what comes next? Compact fluorescent bulbs are the only real alternative right now, but "bulbs" that use light-emitting diodes, or LEDs, are quickly emerging as a challenger. LEDs, which are small chips usually encased in a glass dome the size of a matchstick head, have been in use in electronics for decades to indicate, for example, whether a VCR...