In a sweeping survey of e-books' impact on reading habits, the Pew report said that four times more U.S. readers, or 15 percent, were reading e-books on a typical day now compared with less than two years ago.

But when it comes to reading in bed, the verdict is split. Forty-five percent of those surveyed preferred e-books and 43 percent gave the nod to old-fashioned print.

Lee Rainie, the head of the Pew Internet Project, which conducted the survey, said the results underscored huge cultural and publishing changes as people do more of their book reading online.

"People's relationship to books is a central part of culture. So when that relationship is in transition like it is now, it's an interesting thing to mark," he said.

The e-book industry has grown from $78 million in sales in 2008 to $1.7 billion in 2011, according to Albert Greco, a book industry expert at Fordham University. He has estimated e-book sales will be $3.55 billion in 2012.

Forrester, a consultancy, has forecast that nearly a quarter of Americans will own an e-book reader by 2016. With prices for top models below $100, the readers "are a no-brainer for more and more consumers," it said in a report.

Online retailer Amazon.com Inc has about 65 percent of the e-book market, according to Cowen & Co estimates.

E-READER HOLIDAY

The Pew poll found in February that 21 percent of Americans 18 and older had read an e-book in the previous 12 months, up from 17 percent in December 2011.

The jump was attributed to gifts of digital book readers and tablet computers over the holidays.

People who use e-books are more voracious readers of books of all kinds, with 88 percent of those reading e-books in the previous 12 months also consuming printed books.

They also are more likely to be under the age of 50, have some college education and live in households that make more than $50,000 a year.

The most popular formats for e-book reading are on a computer and on digital readers such as Amazon's Kindle or Barnes & Nobles Inc's Nooks, both at just over 40 percent.

The survey was based on interviews of 2,986 Americans aged 16 and older conducted from November 16 to December 21. Other surveys were held in January and February.

The work was underwritten by a grant from the Bill & Melinda Gates Foundation.

(Additional reporting by Sam Wahba in New York; Editing by Philip Barbara)

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