Kim Kyung-Hoon/Reuters

Sony will soon introduce a visorlike headset, in which 3-D video can fill the visual equivalent of a movie screen. Visitors tried out the new device at an electronics show this month near Tokyo.

But for those who want an even more personal experience, Sony will soon introduce a high-definition, three-dimensional display built into the visor of a headset.

Called a Personal 3D Viewer, this pearly gray visor has two small screens that sit an inch or two in front of the eyes. Pull on the visor as you would a baseball cap, plug the headset into a cable box, game console or Blu-ray player and then watch as high-definition 3-D video fills the visual equivalent of a movie theater screen. The images on the twin screens are made of micron-size pixels that are unnoticeable even from a nose-length away.

The headsets will go on sale in the United States next month for $799, said Charles Speidel, vice president of the Sony Electronics home audio and video group in San Diego. As with other stereoscopic displays, each eye sees a different image — the brain combines them for an illusion of depth.

The headset weighs a bit less than a pound. It leaves enough room inside for eyeglasses (which I wear) and can be adjusted so that not all the weight is resting on the bridge of the nose. Still, I found wearing it a bit cumbersome — until I started watching a demonstration video. Then I was too busy to notice, as I reflexively dodged cars and projectiles hurtling toward me from the screen.

Image quality is excellent on the screens, which measure 0.7 inch diagonally, said Chris Chinnock, president of the marketing firm Insight Media, who has tried the new device at trade shows. "But you are still wearing this bulky headset," he added.

The screens are made of organic light-emitting diodes that glow when a current passes through them, creating bright colors and deep blacks.

The Sony headset was designed with the home theater fan in mind — it does not plug into an iPad, or iPhone, although it will work with one Android tablet, said Rob Manfredo, a Sony spokesman.

If you want a more portable 3-D headset, plug the Vuzix Wrap 1200 ($499) into your iPhone, iPad, Android or portable gaming device — or even into your PC — and watch both 2-D and 3-D video, though not in high definition. (This headset is designed to look like sunglasses.)

As yet, there isn't a vast array of 3-D entertainment to watch on headsets — a situation likely to deter many consumers, said Carolina Milanesi, an analyst based in London for the research firm Gartner. "People aren't going to rush to buy hardware if there isn't anything much to watch," she said.

The number of quality 3-D movies and games is still relatively small. Owners will be able to plug the Sony headset into a cable box and watch college football in 3-D on ESPN 3D, or into a game system or 3-D Blu-ray player, Mr. Manfredo said. There are about 85 Blu-ray movies in 3-D, he said, including "The Lion King," "Pirates of the Caribbean: On Stranger Tides" and "Avatar."

The headset is wired to a hand-size control box that plugs into a set-top box or any other source of 3-D content via an HDMI cable, which carries data fast enough for 3-D signals. Viewers can also watch in 2-D on the headset.

Mr. Speidel of Sony says the headset isn't meant for viewers who are 15 or younger, in part because its dimensions are better suited to adult-size heads.

In addition, it might not be good for youngsters' eyes, he said. "At that age, children's eyes are still developing," he said. "It's a new technology and kids spend a lot of time gaming." When viewers turn on the set, Mr. Manfredo said, they will see a recommendation to spare young eyes.

Dr. David G. Hunter, ophthalmologist in chief at Children's Hospital Boston and a professor at Harvard Medical School, said that most visual development happens before age 7 or 8.

"That's when something could potentially go wrong if you were wearing these for all of your waking hours," Dr. Hunter said.

He had this practical advice for people of any age who are concerned about eyestrain: "Common sense dictates that if the headset bothers your eyes, you should take it off."

A DIFFERENT hazard concerned Sherry Turkle, a professor at the Massachusetts Institute of Technology and author of "Alone Together: Why We Expect More From Technology and Less From Each Other."

Gadgets like 3-D headsets are seductive, she said, but the danger is that they seal people off from their environment and from others.

"People used to walk with eyes to the sand and water," she said, using the example of people strolling at the seashore. "Now everyone walks with a device. No one is looking at the sand."

She has reservations about the technology that has produced immersive personal devices like music players, smartphones and video headsets.

"The technology which looked so good 15 to 20 years ago," she said, "now looks like it helps us miss out on the complexities and grittiness and ups and downs of what real life has to offer."