Japan’s push to keep power flowing after it shuttered its nuclear program may best be illustrated by 73 million light bulbs.

That’s the number of LED bulbs sold in Japan since the start of 2012, representing about 30 percent of the total. The LEDs, which consume a fifth of the energy used by standard lights, are key to the nation’s strategy to make energy use more efficient, even as it pursues alternative sources such as solar power.

Four years after the Fukushima nuclear meltdown spurred the idling of all its reactors, knocking out 30 percent of the nation’s power supply, the drive to reduce energy consumption has sparked a national campaign that includes everything from improved insulation for homes to train stations powered by the braking of subway cars and vending machines that recycle waste heat and generate power with solar panels on top.

“There’s no doubt Japan has some of the most advanced technologies in energy-saving,” said Takumi Fujinami, a senior researcher at Japan Research Institute. “And there is still room for saving energy dramatically.”

Since Fukushima, the nation’s utilities have been forced to fire up older power plants that rely on fossil fuels. That’s helped make up for some of the lost capacity, but not all. The decision to cut consumption was a natural ally in the effort.

Hiroshi Amano, who shared last year’s Nobel Prize for physics, sees LEDs playing an even bigger role. Japan could cut annual electric spending by as much as ¥1 trillion ($8.4 billion) within five years by using more LEDs, according to Amano, one of three Japan-born scientists who were awarded the Nobel Prize in 2014 for their work developing the blue LED.

While LEDs cost as much as $10 apiece, compared with as little as 70 cents for incandescent bulbs, the fact that they’re more efficient “can extend shelf life and reduce the total cost and power use,” Amano told reporters last month.

LEDs, or light-emitting diodes, are built using semiconductors that allow passage of electrons through the material to produce light, requiring less energy than incandescent bulbs, which must heat a wire filament until it glows.

LED sales in Japan reached $5.2 billion in 2013, according to an October report from the International Energy Agency. Switching all of Japan’s lighting to LEDs would save about 92.2 terawatt-hours of electricity, or 9 percent of its total annual consumption, the Institute of Energy Economics, Japan, estimated in 2011.

Japan is pursuing a variety of alternatives after shuttering its nuclear plants for safety checks, pulling 47 gigawatts of capacity from the grid. Subsidies for solar power, which are triple what Germany offers, have made Japan the biggest market for the technology in the world behind China. The country may install as much as 12 gigawatts of solar panels this year, according to Bloomberg New Energy Finance.

The options run from old standbys such as making sure homes are insulated to ideas that offer a unique take on how to keep usage under control.

The government has set a goal for all new public buildings and homes to be net-zero energy by 2030, meaning they use only as much energy as they can produce from renewable sources and other on-site generation systems. About 40 percent of existing homes have no insulation, according to a December task force report.

In the meantime, Mitsubishi Electric Corp. said in September that a system installed at a Tokyo subway station to harvest energy generated by braking subway trains saved enough to run 60 homes. The power is being used for station lighting, air conditioning and elevators, the company said.

All of these efforts are apparently paying off, according to a task force on power demand for the trade ministry.

Power used by the nation’s nine regional utilities fell by 10 terawatt-hours in July and August, thanks to conservation measures, compared with the same period before the Fukushima disaster, the task force found. Overall for the fiscal year ending March 31, consumption fell in eight of the first nine months, with declines ranging from 1 percent to 8 percent.

Results from the consumption campaign are also being felt within the industrial community.

Komatsu Ltd., the world’s second-largest producer of construction equipment, is among companies working to reduce electricity use at production sites. An assembly plant that opened in May in Ishikawa Prefecture consolidates two old plants and is designed to halve electricity use by incorporating such technologies as energy storage and LED lighting.

“We had been working to cut the power use by half after the Fukushima earthquake and it turned out the efforts also led to better productivity,” said Hiroshi Ishihara, a Komatsu spokesman. Komatsu reduced total electricity use by 38 percent in fiscal 2013 from 2010.

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