Starting next week, when the wipers on the car go swish, swish, swish, the car's headlights better go shine, shine, shine, or else.

A new Pennsylvania law, effective Monday, requires motorists to turn on their headlights whenever they run the windshield wipers, even intermittently, due to rain, snow, sleet, mist, or other inclement weather. Violators can be pulled over and fined $25.

It seems like a no-brainer: Can't see. Turn on lights.

Yet "sometimes it takes a law to prompt people to do something that makes them safer," Catherine Rossi, spokeswoman for AAA Mid-Atlantic, said.

The law's language is a little foggy, however. Because it does not explicitly require full headlamps, daytime running lights - not to be confused with parking lights - are acceptable, Trooper Lynette Quinn, public-information coordinator for the state police, said.

Tail lights on some cars do not illuminate when running lights are engaged, so "for best practice, turn your headlights on completely," Quinn urged.

In 2005, more than one-fifth of the 133,000 crashes on Pennsylvania roads occurred during poor weather, according to the most recent data available from the state Department of Transportation.

Pennsylvania joins New Jersey and at least 14 other states with similar legislation, according to the AAA national office.

This week, many drivers were still in the dark but not without opinion.

"I guess it's good for visibility," said Daniel Brown, 33, of Philadelphia.

Paul Dunn, 44, of West Chester, also was unaware. "It's starting to sound like a police state around here," he said, as he gassed up his car. "It's another reason to pull you over."

If this winter ever gets serious, Dunn will have one more new safety measure to live with. Effective last May, motorists can be fined up to $1,000 if snow or ice from their vehicle causes injury or property damage.

Contact staff writer Lini S. Kadaba at 610-701-7624 or lkadaba@phillynews.com.