http://www.bbc.co.uk/news/health-30574260
The article, however is not talking about electronic readers it's talking about using a tablet instead of an electronic reader.
It's a very badly written article.
"The researchers said other e-readers such as the Nook and Kindle Fire produced similar wavelengths of light and would have the same impact."
Some Nooks do not produce similar wavelengths of light.