the country can do it too. >> that's a lot of potential there. >> tons of potential. and really i think one of the things that we like to do is in chicago is we like to experiment and pilot things and then figure out how does that become a systemic change. >> reporter: los angeles has installed about half of the amount of lights as chicago, and some smaller cities like tucson have already made the switch. other cities like philadelphia, boston and pittsburgh are currently developing their streetlight modernization plans. with chicago now signing in a new light, the energy cost of industry lights has already been cut in half from last year, charting a greener future for america's third largest city. >> it compels us to look at what other parts of our infrastructure can we think about in this way. are there other public/private partnerships that can deliver on this? these are the kinds of futures i think that a project like this provokes. >> that was nbc's mara barrett reporting. next, an update.