A billboard that promotes energy efficiency has been lit up by 40 400-watt lamps for about nine hours a night since February.
The ad, on the side of Auckland's Downtown Shopping Centre, is one of five for Right House, a subsidiary of Meridian Energy. A sixth is going up in Wellington next week.
The billboard is due to come down next month and the Government's Energy Efficiency and Conservation Authority estimates the power used during the three-month campaign will cost up to $2600, enough to power the average four-bedroom home for about a year.
A Right House spokesman says the campaign aims to promote energy-efficient homes using as few sites as possible. The alternative to the downtown Auckland billboard would have been several other smaller sites around the city, which would have used more power.
Right House isn't the only firm under the spotlight for energy use in the run-up to yesterday's worldwide power-saving initiative Earth Hour.
Businesses around New Zealand switched off lights for 60 minutes at 8pm to draw attention to the amount of power wasted.
Despite the threat of winter power cuts, top businesses and New Zealand's leading university seem unable to find the "off" switch.
And the EECA says millions of dollars are wasted by companies which leave lights blazing in buildings when no one's at work.
They say Auckland businesses spend $50 million a year on lighting, with further millions frittered away as computer monitors and photocopiers hum through the night.
The Herald on Sunday captured evidence in a string of photos taken after midnight on three days this month, with Auckland University's business school one of the worst culprits. A spokesman said cleaners were in the state-of-the-art building from 10.30pm to 2am, and some external and internal security lights operated during darkness.
But he had no explanation as to why almost the whole building was lit up at 1.15am on a Saturday.
The university has an environmental policy and last year appointed an environmental co-ordinator. Its website says it's committed to pursuing "environmental excellence" and to lead the country in being green.
Good energy management has allowed the university to keep its "relative" electricity use at a similar level to 30 years ago, the website says.
But its actual use is rising at 6 per cent a year, an increase blamed in part on 13,000 computers.
There were full marks for Mighty River Power, whose Greenlane HQ was in darkness when we called, but not every power company can boast the same record.
At the Newmarket headquarters of network company Vector, lights blazed across two floors with nobody visible when we visited just after midnight.
A spokeswoman said the building was operational 24 hours a day but Vector's website recommends keeping lights on only "in rooms you're in".
Computers should be switched off when not in use and monitors should be turned off if you leave your workstation for more than 15 minutes, the website adds.
Energy Efficiency and Conservation Authority chief executive Mike Underhill said businesses should think more about saving power.
"Even if you have people working in an office for 12 hours a day, if you are leaving your lights on overnight, that is still 12 hours of wastage."
In large offices often no one is responsible for switching off lights. "Investing in a system with motion sensor technology takes care of this and will pay for itself over time."
Lights aside, businesses were guilty of wasting power in other ways.
"When the lights are left on, it's obvious. But businesses should also think about all the other equipment that could be left on that is not so noticeable, like photocopiers, printers and computers, all sucking up electricity when no one is there."
The Right House spokesman said it had done everything possible to save power. One site in its campaign uses solar power and another has sodium vapour lights requiring about a third of the power as most billboards.
The Earth Hour initiative, which started in Sydney last year, ran from 8pm yesterday.
In Christchurch and Wellington, city councils were to show their support by switching off external lighting at swimming pools, libraries, recreation centres and other municipal sites.
Energy use dropped by 10 per cent in Sydney last year. Lights were switched off at the opera house, the harbour bridge and homes.By Alice Hudson Email Alice