Here's the perception, left over from the olden days of media. One medium's gain is another's loss. So if TV viewership was rising, as it was for so many years, then fewer people must be listening to less radio or reading fewer newspapers.

Now apply that zero-sum thinking to digital media: More people watching TV online must mean fewer are watching TV on their TV sets.

Funny thing is, though, it's simply not true.

Rather than luring viewers away from their TV sets, new media options like the internet and for that matter cell phones--mobile video--are adding to the total amount of TV watching, according to a new report from Nielsen.

In fact, those other viewing options may actually be increasing the amount of TV watched on TV sets.

As it turns out, even with the rising popularity of internet and mobile video, the number of people watching TV on TV sets rose 1.6 percent in the third quarter, averaging 282 million people. The average person watched more than 142 hours of TV in an average month, up five and a half hours from the year-earlier period.

Some of this is due to NBC’s Summer Olympics, which aired during that time. But viewing was trending up prior to the Games. The average person watched 140 hours in second quarter, compared to 137 hours in third-quarter 2007.

What it really comes down to is simply more television to watch, with more than 100 channels in most homes, and more ways to watch it.

That includes delayed viewing, which allows people to watch more of their favorite programs. Of the 282 million people who watched TV in third quarter, nearly 68 million watched an average six and a half hours of time-shifted TV – DVR playback or video on demand.

And while it would seem to make sense that at some point the newer media would begin cutting into traditional TV watching, that too appears not to be the case, at least not any time soon.

“I don’t really see anything cutting into TV viewing anytime soon, at least for adults,” says Steve Sternberg, executive vice president of audience analysis at media buying agency Magna.

“Given that around 80 percent of homes have only one TV set on during primetime, TV set viewing largely remains a group activity while online and mobile are singular activities.”

During third quarter, more than 120 million people watched internet video, up from 119 million in second quarter, but they watched it for less time, on average two and a half hours a month versus more than 140 hours of traditional TV. Only 10 million people watched videos on their cell phones in third quarter for an average 3 hours and 37 minutes per month.

It’s also likely that much of this internet video watching is taking place at work, with viewers catching up on missed shows. The demographic groups that watch the most internet video are working-age adults 18-24 and 25-34, at about four hours and three hours and 20 minutes in an average month, respectively.

“When people are at home, watching from a TV screen is still the primary source and that’s not going to change,” says Shari Anne Brill, senior vice president and director of programming at Carat.

That will only begin to change when the quality of the online experience improves, such that the internet ceases being a second-choice medium and becomes an alternative to the TV set.

“When the quality and ease of online and mobile [video] comes close to equaling regular viewing on the set, we’ll see a lot of fragmentation,” says David Scardino, entertainment specialist at RPA in Santa Monica, Calif. “But, right now, that’s far from the case.”