Conventional wisdom is that daylight-saving time saves energy. It stays lighter an extra hour in the evenings, so you don't need as much electricity to light your home. When Congress extended daylight saving by a month starting last year, it was a move to cut energy use. California has even petitioned Congress for federal "approval" to go to a year-round daylight-saving plan in an effort to save energy.
But there's new evidence suggesting the conventional wisdom is wrong, and that we might be using even more energy during daylight-saving months. According to the Wall Street Journal :
[The] research showed that while an extra hour of daylight in the evenings may mean less electricity is spent on lights, it also means that houses are warmer in the summer when people come home from work. Conversely, during daylight-saving time's cooler months, people may crank up the thermostats more in the morning.
You can thank Indiana for this data. That state -- which historically utilized daylight-saving time on a county-by-county basis -- adopted a statewide daylight-saving in the spring of 2006. That provided researchers with a nifty way to measure the impact of changing time.
Their finding: Having the entire state switch to daylight-saving time each year, rather than stay on standard time, costs Indiana households an additional $8.6 million in electricity bills.