A Harvard Medical School research team compared reading real books with e-readers before sleeping. According to their studies, it was difficult to put down an e-reader rather than a real book, which led to poor quality of sleep and being more tired the next morning.

However, the team makes an exception for the original Kindle, which does not emit light.

The test used 12 people locked in a sleep laboratory for two weeks. They had five days reading paperbacks and five days reading from an iPad.

Their iPad test blood samples showed that melatonin’s production had been slowed and their subjects had a lower level of melatonin.

The spread of smartphones in the mainstream market had exposed people’s eyes to LED lights even before they sleep. E-readers are more at risk of these nocturnal problems if they do not regulate their reading activities.

The human body uses the body’s internal clock to keep in tune with the rhythm of   night and day. It uses light to tell the time. However, the blue light, common in most smartphone and tablet LED could disrupt the body’s internal clock by slowing down the production of the sleep hormone melatonin.

According to Lead Researcher Professor Charles Czeisler  “The light emitted by most e-readers is shining directly into the eyes of the reader, whereas from a printed book or the original Kindle, the reader is only exposed to reflected light from the pages of the book.”