Coastlines globally are increasingly being illuminated with Artificial Light At Night (ALAN) from various urban infrastructures such as houses, offices, piers, roads, ports and dockyards. Artificial sky glow can now be detected above 22% of the world’s coasts nightly and will dramatically increase as coastal human populations more than double by the year 2060. One of the clearest demonstrations that we have entered another epoch, the urbanocene, is the prevalence of ALAN visible from space.Photobiological life history adaptations to the moon and sun are near ubiquitous in the surface ocean (0-200m), such that cycles and gradients of light intensity and spectra are major structuring factors in marine ecosystems. The potential for ALAN to reshape the ecology of coastal habitats by interfering with natural light cycles and the biological processes they inform is increasingly recognized and is an emergent focus for research.In this paper we derive a methodology to quantify and map the depths to which biologically relevant ALAN penetrates in the marine environment. We use two satellite derived global datasets to achieve this: an artificial night sky brightness world atlas (Falchi et al., 2016) and an in-water Inherent Optical Property (Lee et al., 2002) dataset derived from ESA’s Ocean Colour Climate Change Initiative (OC-CCI https://www.oceancolour.org/). These primary datasets are both used in conjunction with in-situ derived measurements and radiative transfer modelling in order to quantify the critical depth (Zc) to which biologically relevant ALAN penetrates throughout the global ocean’s estuarine, coastal and near shore regions, in particular the area defined by an individual country’s Exclusive Economic Zone.