Green lighting = energy-efficient lighting = significantly lower public lighting costs. Every city in the U.S. that can afford these upgrades is doing them [[see Ann Arbor for a local example). The federal government has been putting money towards energy efficiency projects for decades because it is in the national interest, and because these projects reduce the need for new power generation facilities [[typically heavily subsidized as well). It's really just a shift of the subsidy from a supply-side, power generation model to a demand-side energy-efficiency model. The added bonus is that we prevent air pollution, GHG-emissions, and hazardous waste creation by controlling demand. Hence, the "green" label.