For the past decade, scientists have been exploring whether artificial light — particularly wavelengths of blue light — poses a risk to human health.

You may have heard that too much screen time in the evening is a bad for you, and it’s true the blue light emitted by devices like phones and tablets can disturb your sleep.

But blue light is not all bad — and here’s why.

Blind mice sense blue light
In 2002, scientists identified a new type of photoreceptor cell in the eye, when the visually blind mice they were studying were still able to respond to certain wavelengths of light.

The light spectrum with nanometres marked.
Intrinsically Photosensitive Retinal Ganglion Cells in the human eye are most sensitive to light wavelengths of 480 nanometres. (Wikimedia Commons: Fulvio314)
The cells, called Intrinsically Photosensitive Retinal Ganglion Cells (ipRGCs) respond to light for regulating our circadian clock — not for forming images like the rods and cones in our eyes do.

By detecting how much light is in our environment, the cells can communicate to our brain and body that it’s day-time, or that it’s time to sleep, thereby setting our circadian clock, according to neuroscientist Stuart Peirson from the University of Oxford.

“We’ve evolved to expect light during a particular part of the day and that optimises our physiology and behaviour to anticipate changes in our environment,” Dr Peirson said.

IpRGCs are most sensitive to light wavelengths of 480 nanometres — right in the blue light spectrum.

But Dr Peirson said in actual fact, IpRGCs can detect most wavelengths of light, and it can all disrupt our circadian clock.