They found it took longer to nod off with a back-lit e-reader, which led to poorer quality sleep and being more tired the next morning.
Original Kindle readers do not emit light so should be fine, say experts.
Experts said people should minimise light-exposure in the evening.
Whether you are perusing the Man Booker shortlist or leafing through Zoella, the impact of reading on your sleep is probably the last thing on your mind.
But there has been growing concern about the dangers of light before bedtime.