Concrete is not even close to the number one source of carbon emissions. It accounts for roughly 3% of total emissions, which is about 1/4 the amount that road transportation emits.

If we stopped using concrete completely, alone this action would have pretty much no measurable effect on our C02 problem. Although it could be part of the mosaic of solutions and that is worth saying.

https://en.wikipedia.org/wiki/Orders_of_magnitude_(illuminance)

Here are the numbers. I can verify that you can hike rough terrain and read large lettering by Moonlight. This was especially true in the winter with leaves off the trees and snow on the ground reflecting the light. But I did not find this to be the case for starlight but it was most definitely not pitch black like a cave. So I hesitantly agree with you.