Daylight saving time! What is it good for?

Not much, say two University of California, Santa Barbara researchers who conclude that setting the clock forward actually ends up using more energy, not less.

"I've never had a paper with such a clear and unambiguous finding as this," lead researcher Matthew Kotchen told the Wall Street Journal.

One big argument for daylight saving time, which began as a temporary measure during World War I and gradually became a yearly fixture in most of the U.S., has always been that more daylight in the afternoon reduces the need for artificial lighting, thus cutting down on energy costs.

That's the main reason why Congress, in the 2005 Energy Policy Act, extended daylight saving time to begin the second Sunday in March and end the first Sunday in November. Standard time is now not standard at all, covering only one-third of the calendar year.

But, as Kotchen, an economics professor, and doctoral student Laura Grant explained to the National Bureau of Economic Research last month, that's bunk.

"There is surprisingly little evidence that DST actually saves energy," they state in the abstract to their draft paper. "Our main finding is that — contrary to the policy's intent — DST increases residential electricity demand."

• Click here to read the draft paper (PDF).

The pair were given a unique opportunity to test the energy efficacy of daylight saving time when most of Indiana's counties, which had long held out against the practice due to farmers who didn't want to plow fields in darkness, finally relented and instituted it in 2006.

They compared 2006's energy-use figures in the 77 affected counties with energy use in the years before the switch.

For controls — an experiment always needs a control — they had the 15 Indiana counties, scattered around the state's corners, that had practiced daylight saving time before 2006.

The result? While there was initially a bit of energy savings in the early spring, that was offset by much greater use of energy in late summer and fall — $8.6 million more, in fact.

The big difference, it turns out, is air conditioning, which only the very rich could afford at home before World War II and hence never figured into the calculations of daylight-saving-time's proponents.

Getting home earlier in the afternoon, as far as the sun is concerned, means more heat and demand for cranking up the A.C.

That's one reason power companies worry about summer blackouts in the late afternoon and early evening on hot days, as schoolchildren and early risers get home even as office buildings continue to be occupied for several more hours.

Kotchen and Grant concede there are some societal benefits to daylight saving time — everyone likes more daylight — but conclude that the whole idea needs to be re-examined.

"We find that the longstanding rationale for DST is questionable, and that if anything the policy seems to have the opposite of its intended effect," they write.

• Click here to read the full article in the Wall Street Journal.