The organisers of Lights Out London certainly think so, and they have the mayor, Capital Radio and a host of mid-range celebrities (Johnny Vaughan, Sophie-Ellis Bextor) to back them up. The idea is that on June 21 as many Londoners as possible will turn off non-essential lights between the hours of 9pm and 10pm. Buckingham Palace, Canary Wharf, Harrods and other famous buildings have agreed to join in.

The gesture, designed to raise awareness of electricity use, follows similar experiments in Sydney, Paris and Hong Kong. It is said that if all 3m households in London switch off unnecessary lights for an hour it will save 380 tonnes of carbon dioxide, enough to fill the proverbial Albert Hall.

A previous proposal for a national switch-off, backed by Al Gore, was shelved when it was explained that the large, unpredictable change in demand might do more harm than good, as in those circumstances the National Grid would have to run extra power stations to guarantee supply to essential services.

Thankfully, there would be no such problems with a "small" area such as London. But even if everyone in the city takes part, how much good will 380 tonnes less carbon dioxide actually do to the planet? The answer, of course, is not enough.

"In most homes," a spokesperson at the Energy Savings Trust points out, "lighting accounts for 10-15% of the electricity bill. Any initiative that helps consumers to be more aware of the energy they are using is a good thing. However, we would also encourage consumers to think about saving energy in the longer term."

According to the trust, if every household in Britain swapped one normal light bulb for an energy-saving one, it would save enough carbon dioxide to fill, ahem, 2,000 Albert Halls.