A leading doctor has argued that technology such as smartphones should have a "bedtime mode", Digital Spy said.

Professor Paul Gringras, from Evelina Children's Hospital in London, has said that the setting should filter out the blue light that keeps people awake later in the evening.

Certain wavelengths of light can disrupt the body producing sleep hormone melatonin, which it starts to do as it gets darker in the day.

The doctor was part of a study published in Frontiers in Public Health which analysed the light emitted by devices such as smartphones, tablets and e-readers. It concluded that there was a clear trend for new devices to be bigger, brighter, have higher levels of contrast and emit more blue light.

"That is great for us in the day, but awful for use at night," Prof Gringas told BBC News. "There is converging data to say if you are in front of one of these devices at night-time, it could prevent you falling asleep by an extra hour."

He added that some sleep-aware apps had been designed, but that there needed to be "more responsibility from manufacturers" and the "key is to automate it".

"It's not good enough to say do less and accept this is the world we live in," Prof Gringas concluded. "They're fun devices, but we do need some protection on what they do at night-time."