> instead of shutting down agriculture in the only marginal spot on the west coast you can grow food.
Not an expert, but I would think greenhouse light pollution is not necessary for agriculture? It seems like obvious waste (money spent generating light that isn't going to photosynthesis), but I assume it's cheaper not to shield the lights than to shield them, so it's a matter of ROI and requiring people take care of their externalities.
Is there an economic argument that light shields will make agriculture in that area too expensive?
I mean it's not easy to have greenhouse walls that let sunlight in but don't let grow light out. You can direct the light but you are going to have loss.