You can see most large metropoles having a white core. In Rotterdam and The Hague (Netherlands), this white core is in between.

Very interesting. I live on the southern outskirts of The Hague, Netherlands. Between The Hague and De Nieuwe Waterweg is the Glass City [0] located, a large area (~20x20km) with mainly greenhouses. These greenhouses use artificial light to spur growth in plants, causing the white core in the light pollution heatmap.

When I look out on my balcony to the south, the sky never turns dark. Only when there is heavy rain clouds, the light from the greenhouses dims a bit. The sky is always in an orang-y darkish glow.

[0]: https://translate.google.nl/translate?sl=auto&tl=en&js=y&pre... (translated dutch wiki page, english page is only stub)