We sleep two hours less these days

In the West we sleep around two hours fewer per day than we did a century ago because of another consequence of modern living: electric light. The bluish light emitted from screens is pernicious when it comes to disrupting sleep, because the brain interprets it as morning. To expose yourself to blue light every evening is to risk mild and persistent jetlag, as your body clock tries to adjust in response to this ‘morning light’. The sleep clinic to which I send patients in Edinburgh prescribes orange filters for the use of screens in the evening: they translate the pixillated light into the colours the brain associates with sunset and firelight.