A study conducted by researchers from the University of Plymouth and Plymouth Marine Laboratory, who have spent more than a decade examining the impact of artificial light at night (ALAN) on the world’s coasts and oceans, has shown that more than one-fifth of the global ocean – an area spanning more than 75million sq km – has been the subject of ocean darkening over the past two decades. Ocean darkening occurs when changes in the optical properties of the ocean reduce the depth of its photic zones, home to 90% of all marine life and places where sunlight and moonlight drive ecological interactions.