It's a book. No, it's a reading light. Ah, it's both -- it's the latest Barnes & Noble Nook.

On Thursday, the U.S.'s largest bookseller announced its Nook Simple Touch with GlowLight, which it describes as the "world's first and only E Ink reader that lets you read in the dark."

'No. 1 Problem' in Bed

Distilling relationship issues to a single functional challenge, Barnes & Noble said the new device eliminates "the No. 1 problem couples have in bed," which, it ventured, was one person reading with the light on, and the other trying to sleep.

Apparently, couples counselors everywhere will be relieved to know that the GlowLight resolves that central issue by providing a built-in adjustable reading light. According to Barnes & Noble, 64 percent of adult readers regularly read in bed.

William J. Lynch, Barnes & Noble CEO, said in a statement that, to date, readers have had to compromise by either "buying black-and-white E Ink reading devices to optimize their outdoor reading or color LCD devices to be able to read at night in bed with the light off."

Or, as Ross Rubin, executive director of connected intelligence at the NPD Group put it, the new device is "bookworm meets glowworm."

He noted that Barnes & Noble took about 18 months to develop this solution, which required keeping the device thin and lightweight. Rubin added that the ability for e-readers to work well both at the beach and in a darkened room "will probably become a popular option" over the long term for many e-readers.

The new Simple Touch is also the lightest Nook yet, and the battery is designed to power the device for one month of reading for a half-hour a day on a single charge, even with the light on.

Shifting E-Book Market

This combination of the E Ink display with an anti-glare screen and an adjustable light is the bookseller's attempt to carve out a competitive nook for its e-reader, as the market for e-reading takes off and changes.

Barnes & Noble is trying to maintain its position, which is about 30 percent of the e-book market, compared with Amazon's 60 percent.

In addition to the jockeying on the hardware side, the pricing of e-books is in the process of changing again. Two years ago, in an effort to counter Amazon's selling of some e-books at a loss to gain market share, Apple and six major publishers agreed to an "agency model," where retailers were prevented from discounting e-books. That helped Barnes & Noble, which can less afford to sell e-books at a loss or even reduced prices, than Amazon.

But now the U.S. Department of Justice, and several states, have sued Apple and the publishers, on charges of price fixing. Several publishers have settled, and the terms include an end to the agency model. From Barnes & Noble's point of view, that could put it at a disadvantage, since Amazon will likely be in a better position to cut its e-book prices.