These last few weeks, it was no longer pitch dark for his daily 5:15 a.m. run. And yesterday, when the financial analyst caught his 6:18 train from Jenkintown to Center City - six minutes before sunrise - the sky had lightened to a pearly gray.

But tomorrow morning - wham! - nature's gift will be snatched away and tacked on in the evening, thanks to a few strokes of the legislative pen.

"I'll be running in the dark again for another month," lamented Lang, who works at 20th and Market Streets.

Yes, it's the second year of a national experiment to save energy with an earlier start for daylight saving time.

The theory: If we're awake for more of the daylight, we'll have the lights on for less time. So if we start it sooner - four weeks earlier this year - we might save even more.

Within the next few months, the U.S. Department of Energy is expected to report on whether that more-is-better theory held true in 2007. Yet a new study, by economists at the University of California, Santa Barbara, suggests it might make sense not to do daylight saving at all.

For their research, presented at a conference last month, the authors analyzed residential electric bills in Indiana from 2004 through 2006. The state offered a ready-made, real-life experiment: In the first two years, some Hoosier counties did not use daylight saving, but in 2006, they all did.

The conclusion: While the shift may save electricity because of reduced demand for lighting, the gains are apparently outweighed by increased electricity use for heating and cooling. In the summer, for example, people are awake for more of the daylight, the period during which they are likely to have their air conditioners on a cooler setting, said lead author Matthew J. Kotchen.

The net costs: an increase of 1 percent to 4 percent, Kotchen said. But he is quick to add that he isn't advocating the end of daylight saving. There are other benefits, such as the extra time in the evening for outdoor activity.

"I personally like daylight savings time," Kotchen said. "If we're going to do it, let's do it for the right reasons, and not the wrong reasons."

One thing researchers do know, on the other hand, is how the time shift affects one of our most primal regulatory systems: the body clock.

There's an impact whether we "spring forward" on the first Sunday in April or, as we do this year, on the second Sunday in March, said George Brainard, a professor of neurology at Jefferson Medical College.

The annual switch has the potential to affect our bodies in two ways, said Brainard, a leading expert on the impacts of light on the body's daily rhythms. First, many people, rather than curtailing their waking activities, will simply lose an hour of sleep tonight, he said.

A few studies have linked this deprivation to an increase in car accidents for several days after the switch, though the evidence is inconclusive.

Second, some people may experience mild forms of the sort of malaise that comes with jet lag, Brainard said. That's because our physiological clocks take their cues from sunlight, via special cells in the eye. These cells relay messages to the brain about when to adjust hormone levels and rev up the body for the day's activity.

"Light is such a powerful stimulus, even though it's often below our level of consciousness," Brainard said.

No one has studied the bodily effects of starting daylight saving even earlier, he said.

The whole concept matters little to Mike Green, another commuter at the Jenkintown train station yesterday.

He takes the 5:25 a.m. train from Doylestown to Jenkintown, then switches to an outbound train to reach his job as a paramedic in Huntingdon Valley. He always wakes up at 3:30.

"It's dark when I leave," Green said with a shrug, "dark when I get home."

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