On Friday, government-imposed limits take effect aiming to cut electricity consumption by 15 percent in the Tokyo and Tohoku regions, three months after a tsunami sent nuclear reactors into meltdown at the Fukushima Daiichi plant.

The power-saving drive, which for many began shortly after the huge March 11 quake and tsunami but which becomes official Friday, will last through the peak summer months to September to cut blackout risks after the loss of capacity.

Many will have to change how they work as the electricity-hungry nation swelters this summer due to the first such restrictions on power use since the 1974 oil crisis.

Firms that do not cut consumption face fines.

"If it gets any hotter I will not be able to work. I can only wear lighter clothes to cope with the heat," said office worker Masayo Minami, 37, in Tokyo's Ginza shopping district, where on Thursday undeterred boutiques belched out freezing cold air conditioning.

But many have embraced "setsuden", or electricity saving. Japan has taken its annual summer "Cool Biz" campaign -- aimed at limiting air conditioner use and encouraging workers to ditch jackets and ties -- to a new level.

Local governments have prohibited overtime and factories have changed shifts to make use of cooler evenings, early mornings and lower-demand weekends. In one region, employees have been told to take a two-hour siesta after lunch.

Imports of electrical fans through Tokyo's port hit a record high in May, jumping 70 percent from a year earlier to 1.24 million units, according to the customs office.

Workers are also being encouraged to take longer summer holidays in a nation where vacations are regarded as an inconvenience to colleagues.

Yet success in part depends on how high the mercury rises, say analysts.

On Wednesday temperatures soared to 35 degrees Celsius in Tokyo and air conditioner use pushed consumption to 93 percent of capacity, raising fears that the capital may yet face blackouts as the summer heats up.

"We think that power savings will be fairly successful; those savings and the reorganization of rotas can achieve a lot," said Ben Wedmore, director of equity research at MFGlobal in Tokyo.

But "we cannot be completely confident," he added.

Tokyo Electric Power Co, operator of the quake-stricken Fukushima Daini and Daiichi nuclear plants which before March 11 were a key power source for the capital, has raced to reactivate mothballed thermal power stations.

TEPCO's ability to buy power from other utilities is limited by the fact that Western Japan uses a different electrical frequency from the east.

But even utilities not directly affected by the earthquake and tsunami have not restarted reactors that were undergoing maintenance at the time, due to objections from local governments amid a wave of anti-nuclear sentiment.

Only 19 of Japan's 54 reactors are now operating, with more due to shut down for regular checks.

The government has warned of power shortages across wider areas of a nation that generates about 30 percent of its power from nuclear plants.

However, it is "very hard to gauge" whether the gloomy scenario is being overplayed by authorities, said Wedmore.

"Our theory is that relatively new and well-invested reactors will re-open, while 1970s vintage models stay closed."

Restrictions on power consumption may also slow the country's recovery from recession, after the earthquake and tsunami hammered Japanese production and the economy contracted by an annualised 3.5 percent in January-March.

Industrial output rose at its fastest pace since 1953 in May, but the government has warned this could indicate that firms rushed to boost output before consumption restrictions kick in.

But some hope that as companies find new ways of working this summer, they could shine a light towards a new type of power-saving society as Japan rethinks its energy policy currently centred on cheap nuclear generation.

"It would be a shame not to call the bluff of the nuclear engineers and their 'you need us, and we are the cheapest' slogans," said Wedmore.

Copyright AFP (Agence France-Presse), 2011