The hot-air balloons in “Fiesta in the Sky” will be more radiant and tornadoes featured on “Nova” will be scarier than ever as high definition television signals begin Friday on the Maine Public Broadcasting System.

Maine PBS is launching the first statewide high definition signal with sharper pictures, a widescreen format and better sound.

“It’s clearer. It’s more vivid. It’s completely different from what you’re used to seeing,” said spokeswoman Rhonda Morin.

Effective Friday morning, viewers with high definition televisions will be able to see national PBS programming via antenna on Channel 17.2 or through their cable providers in the Portland and Bangor areas.

Local Maine PBS programming remains available in analog form, as well as in digital format for viewers with a traditional TV set and a box necessary to convert the signal.

Maine PBS, which introduced digital programming five years ago, is now offering high definition programming because of viewer demand, said Gill Maxwell, senior vice president and chief operating officer.

Other commercial programming, including prime-time shows and sporting events, also are available in high definition format, but Maine PBS’ signal is the first to do so statewide thanks to its network of digital towers.

Maxwell estimated that 5,000 Maine PBS viewers already have high definition TVs. But he expects the proportion of high definition sets in Maine’s 500,000 households to grow exponentially in the coming years.

“Before you know it, it’ll be just like cell phones. It wasn’t so long ago that cell phones were something that only a few people had. Now everyone has one, and no one thinks twice about it,” he said.

The shift is already being seen at Circuit City, where 90 percent of televisions 32 inches and bigger being sold are high definition sets, said Ron Gallant, sales manager at the Bangor store.

Within a year or two, the only analog TVs sold will be to people who need a second TV for their camps or cottages, he said.

Maine PBS put the state’s first digital signal over the airwaves in 1999 with a test station in Litchfield. The network of digital towers, which cost $20 million, was completed when the last tower was erected last year in Calais.

Of the money spent on the project, $2 million came from a state appropriation, $7.8 million came from a state bond issue and $1.6 million was federal grant money. The rest, about $9.4 million, was raised by Maine PBS.

The federal government has mandated digital conversion for all TV stations to clear air-wave space for other technologies, including cell phones.

But people with traditional analog sets needn’t worry. The federal government has dictated that analog signals must stay on the air until 2006, or until 85 percent of regional viewers have access to digital TVs or coverter boxes.

If that deadline holds, viewers then would then have to buy converter boxes that would allow them to see digital signals on analog TVs.