By Richard Black
Environment correspondent, BBC News website
Britons are being asked to "leave it off" later this month, to show that cutting home energy use can have an impact on climate change.
The event hopes to make people aware of how energy is wasted
During E-Day, which begins on 27 February, people will be asked to switch off electrical items not in use.
The National Grid will assess what difference it makes to electricity consumption, and power companies will offer support for home insulation.
E-Day builds on the Planet Relief idea developed but later dropped by the BBC.
"We're all using electricity, but we tend to have very little idea about how the amount we're using goes up and down," said Matt Prescott, the scientist and climate campaigner who developed Planet Relief and then E-Day.
"There are a million-and-one things you could be thinking about in relation to curbing climate change; but let's focus here on how the choices we make affect energy use, and try to take some small basic steps in everyday life," he told BBC News.
Planet Relief was first developed as an awareness-raising, comedy-led BBC TV programme.
The BBC justified the decision to drop it after 18 months of development by saying viewers preferred factual or documentary programmes about climate change.
The decision came after poor audiences for Live Earth, and public debate over whether it was the corporation's role to "save the planet".
After having worked with the BBC on Planet Relief, Dr Prescott then elected to see whether he could run the project as a stand-alone entity.
Energy companies, charities involved in climate change, other corporate backers and the National Grid decided to continue their support.
The grid's involvement is crucial. Initially it had been concerned that abrupt changes in demand could overload or disrupt supplies around the country.
The National Grid will be able to see if the campaign affects demand
Now, it will measure consumption during the 24 hours against a "business as usual" forecast, and report back what savings have been achieved.
"We are supporting E-Day because everyone can play their part, and also help to reduce their bills by only using the energy they need," said Joe Kwasnik, global head of the grid's climate change policy.
Supermarket giant Tesco is using the event to offer information and services that could help customers reduce energy use.
Major energy retailers are offering simplified access to the programmes they are obliged to operate under the government's Energy Efficiency Commitment (EEC) and Carbon Emissions Reduction Target (Cert).
People will be able to register their interest in measures such as loft or wall insulation through the E-Day website, and the companies will assess whether registrants are eligible for subsidies, which can be up to 100%.
The event is also backed by the Stop Climate Chaos coalition of charities, whose 50 members include such diverse groups as Christian Aid, Greenpeace and the Royal Society for the Protection of Birds (RSPB).
The E-Day campaign hopes to achieve relatively modest cuts in electricity consumption of 1-3%.
"You have to start from somewhere," commented Matt Prescott, who has been in the vanguard of the campaign to ban incandescent lightbulbs.
"And I thought that if businesses and the government are going to make different decisions (about energy and climate issues) in future, then they need to know there's public support.
"We have 70% of the public saying they accept climate change and wanting to do something about it; but almost everybody feels powerless, and I wanted to find a way of making people feel powerful and that they could change something."
Government policy is to reduce greenhouse gas emissions by 60% by the year 2050, and there is debate over whether this target is strict enough, with some scientists urging tougher targets, in the order of 80%, for developed countries.
There is general acknowledgement that individual actions alone cannot bring cuts of anything like this scale.
"E-day is useful in itself," observed Lord Robert May, a former chair of the Royal Society, who is supporting the event.
"But it is even more useful for its potential to engage people in the larger tasks ahead of us if we are to avoid catastrophic levels of climate change."
E-Day will run for 24 hours from 1800 GMT on 27 February.