Sarah Tew/CNET

What's the No. 1 requested feature people want in an e-ink e-reader?

According to Barnes & Noble, it's an integrated light, which is why the company spent the last two years developing the new $139 Nook Simple Touch with GlowLight, available today for preorder and shipping in early May.

I had a chance to play around with the new Nook at a launch event in New York and, as you can see from the pictures, except for the gray border around the edge, it looks identical to the standard $99 Nook Simple Touch , which remains on the market. However, Barnes & Noble says this new model is slightly lighter (6 percent, to be exact), weighing 6.95 ounces.

Now playing: Watch this: New Nook lights it up

"It was really hard to get the lighting just right so it displays uniformly across the display," Barnes & Noble CEO William Lynch told CNET. "We think people are going to be really happy with how it looks."

Lynch said the technology was designed in-house at Barnes & Noble's office in Palo Alto, Calif., and has a patent pending. It's important to note that the glow technology isn't a backlight but rather a form of front-lighting. You activate the light by holding down the Nook button on the front and shut it off the same way. You can also dim the light to avoid bothering a bed partner who's trying to sleep.

As Jamie Iannone, president of Digital Products at Barnes & Noble, demoed the device, he pointed out that the light actually fades on -- and also fades off. He said that was something he requested, explaining that he didn't want it to be too jarring when people turned the light on in the dark. (I joked that he had a touch of Steve Jobs in him.)

Until now, e-ink's chief selling points have been how readable it is outdoors, even in bright sunlight, and very energy efficient. While the lack of a backlight was touted as reducing eyestrain, the inability to read in the dark or dimly lit environments has always been one of e-ink's weaknesses. You either had to buy a clip-on light or a case that had an integrated flip-out light built into it. Amazon charges $59.99 for its Kindle Touch Lighted Leather Cover.

Barnes & Noble considers its integrated GlowLight as a key differentiating feature. Iannone said that engineers also improved the touch performance in the new product (it's more sensitive and accurate) and handed me a Kindle Touch to play around with for comparison. The new Nook did seem more responsive in my limited time with it; page turns also seemed slightly faster compared with on the Kindle.

In shaving off a little bit of weight from the Nook, Barnes & Noble's engineers didn't change the battery. The company says you can get up to two months of use with Wi-Fi off (based on 30 minutes of reading a day) and up to a month when using the GlowLight (again, this is with Wi-Fi off). Other specs also remained the same. You get 2GB of built-in memory and an expandable memory slot that accepts microSD cards up to 32GB.

In all, this is clearly a smart move for Barnes & Noble, and the integrated light really does work well and displays uniformly across the screen. As Sony found with its early PRS-700 e-reader, it's trickier than it seems to pull something like this off with a touch-screen e-ink display.

Rumor has it that Amazon is also working on an integrated light for its next Kindle. A reporter at TechCrunch recently noted that Amazon had acquired Oy Modilis, a Finnish company that's "the world leader in light-guide technology," and that he'd seen a prototype for an e-ink Kindle with a front-lit display at Lab 126, Amazon's Silicon Valley-based design lab.

A glowing Kindle may very well be on the way, but Barnes & Noble has beaten Amazon to the punch.

The big question, of course, is whether that integrated light will be worth the $40 extra to consumers. Barnes & Noble thinks it will be and presented a slide as part of its presentation, laying out the numbers and value proposition. Cases with integrated lights generally cost more than $40 and while clip-on lights typically cost only around $20, they aren't as an elegant a lighting solution. Barnes & Noble is also throwing in a full-fledged AC adapter for charging the new Nook along with an antiglare screen protector. And Iannone is quick to point out that you don't have to look at any ads on its e-reader (Amazon's Kindle Touch with Special Offers costs $99, but the ad-free version costs $139).

"I think this is going to do really well at this price point," Iannone said. "This is a feature a lot of people are looking for in an e-ink e-reader. It's the number one requested item from our users. It's a killer feature."