To get from Kathmandu to the tiny village in Nepal, Dave Irvine-Halliday spent more than t

wo days. When he arrived, he found villagers working and reading around battery-powered lamps equipped with light-emitting diodes, or LEDs--the same lamps he had left there in 2000.

Irvine-Halliday, an American photonics engineer, was not surprised. He chose to use LED bulbs because they are rugged, portable, long-lived, and, extremely efficient. Each of his lamps produces a useful amount of illumination from just one watt of power. Villagers use them about four hours each night, then top off the battery by pedaling a generator for half an hour. The cool, steady beam is a huge improvement over lamps still common in developing countries. In fact, LEDs have big advantages over familiar incandescent (白炽的) lights as well--so much so that Irvine-Halliday expects LEDs will eventually take over from Thomas Edison's old lightbulb as the world's main source of artificial illumination.

The dawn of LEDs began about 40 years ago, but early LEDs produced red or green glows suitable mainly for displays in digital clocks and calculators. A decade ago, engineers invented a semiconductor crystal made of an aluminum compound that produced a much brighter red light. Around the same time, a Japanese engineer developed the first practical blue LED. This small advance had a huge impact because blue, green, and red LEDs can be combined to create most of the colors of the rainbow, just as that in a color television picture.

These days, high-intensity color LEDs are showing up everywhere such as the traffic lights. The reasons for the rapid switchover are simple. Incandescent bulbs have to be replaced annually, but LED traffic lights should last five to yen years. LEDs also use 80 to 90 percent less electricity than the conventional signals they replace. Collectively, the new traffic lights save at least 400 million kilowatt-hours a year in the United States.

Much bigger savings await if LEDs can supplant Mr. Edison's bulb at the office and in the living room. Creating a white-light LED that is energy-saving, cheap and appealing has proved a tough engineering challenge. But all the major lightbulb makers--including General Electric, Philips, and Osram-Sylvania--are teaming up with semiconductor manufacturers to make it happen.

From the first paragraph, we can see that Dave Irvine-Halliday ______.

A．is a mountain climber

B．went to that village to repair the lamps

C．found the villagers were using the lamps he had given them

D．has visited the small village several times