At the very beginning, he gives a personal experience and how he felt at the time. He says that "I knew night skies in which meteors left smoky trails across sugary spreads of stars". With that being said, what he thought of the skies and how it is, he then connects it with how the nights are needed for us humans. He supports his argument by giving a fact dealing with the World Health Organization, informing us that "working the night shift as a probable human carcinogen".
Besides them, he also mentions the American Medical Association explaining how our bodies need the darkness to produce hormone melatonin. By producing that, it would prevent us getting certain cancers from forming and allowing us to have a good time to sleep. If we weren't able to have dark nights, we would end up having different disorders that won't let us succeed for the working days. The Association considers those disorders "short sleep" or "long light".
Besides of mentioning humans, Paul also mentions how the rest of living things need the nights to survive and allowing the species to migrate to other areas, allowing them to grow. He then connects the information with how around the world is needing it and how impacts everyone.
Finally he then mentins about how most people are trying to save the nights and how the beauty of the darkness would allow everyone to see how amazing it truly is.