Haven: The Prabels' lake house in Chadds Ford

Don't bother looking for an electric light in Bruce and Marianne Prabel's living room — there isn't one. And in the sitting room next to it, the sole lamp is turned on only to ward off burglars.

In the Chadds Ford house the Prabels built with such foresight years ago, sunlight dominates. Even on cloudy days, Bruce Prabel says, natural light is all that is needed to see. It pours in through numerous skylights and 30 sliding-glass-door-size panes of glass.

"You can do that with a contemporary [home]. You never need to turn on the light during the day." says Bruce, 72, a retired chemist.

Artificial light would mar the vistas this long-married couple awake to each day: to the south, a private eight-acre swimmable/fishable/kayakable/canoeable lake, and to the west, 45 acres of permanent open space owned by the Brandywine Conservancy.

"Fox, deer, geese, wild turkey, blue heron, turtles, go down the list, and they're here," he says. Even the occasional bald eagle.

Thirty-two years ago, Bruce and Marianne were making lists of a different sort. It was then that the couple decided to lay down permanent roots in Chadds Ford and build a home for themselves and their two teenage sons. And it was then that they decided to abandon typical heating and cooling systems and venture into the relative unknown of geothermal heating and air conditioning.

In the 1970s, Bruce was traveling for DuPont — the couple and their children had lived in Chicago and in the Los Angeles area. He was eventually transferred to Delaware; the couple said, that's it, no more moving.

"I refused to transfer anymore," he says.

Bruce and Marianne decided to build a house, and spent six months looking for land. After seeing this property, they made an immediate offer. A tough decision, it wasn't.

The planning began — the Prabels are born planners. Case in point: the billiards table on the lower floor of the house.

"Marianne accused me of building the house around the billiards table, but it's true," Bruce says. People don't think about how much room is needed to clear the pool cue when taking a shot, but he did.

They also thought a lot about other things, like putting the boys' bedrooms on the lower level with a sliding-glass door of their own, so they could come and go without seeing their parents all the time. That door also opens up to the lake, says Marianne, 72: "They did their laps in the morning."

The couple put their rooms, like their bedroom and the living room and so on, on the first floor, so as they entered their later years, access would be more convenient. The house is near grade-level, with just one step to get into it.

But every room— upstairs and down, save ancillary rooms like the bathrooms — have at least part of that view. You can't turn around without saying, "Wow!" — or, if you're on the first floor, looking up at the 23-foot-high cathedral ceilings and having the same reaction.

Bruce is very proud of the house's three-zone geothermal component and has compiled information about how much the system has saved them. Their total Peco bill for 2011, covering all energy needs, was $2,831.

The lower floor was built in-ground, reducing heat and energy use. Its low-energy fan circulates air cooled or warmed by the earth with the air upstairs.

The Prabels' aesthetics are a reflection of Marianne: She is a naturalist. A native of Germany who moved to Detroit (where Bruce was born) with her family when she was 16, Marianne has decorated the house with "dead" things that make it come alive: Bittersweet wild vine hangs over a mantel; pinecones peek out of baskets; dried grasses stand in a vase near a glass panel.

"I like a lot of natural colors," she says. Along the west wall, the natural color is green — her enormous potted plants dominate there.

In the kitchen, the theme continues. Bruce covered the cabinets with a Japanese-designed, natural grass-weave wallpaper. The island is larger than most, with baskets of all sizes and shapes hanging above it, and hearkens back to Marianne's memories of Germany and women working together at a huge table. It's comforting, she says: "I like warm things. I wanted this as a working kitchen."

Not surprisingly, the Prabels' grandchildren love visiting from North Carolina, referring to this retreat as Camp Oma and Opa's. Pictures of granddaughters catching fish with a proud grandfather are displayed in the kitchen.

But just how many fish will be caught in the future is a question. Bruce was 39 when he planned this house, and, no matter how much foresight you have, he says, you can't predict what it will be like caring for such a large property at his age. He speaks about friends who have died or gone to nursing homes.

"It's way more than we need," he says.