Light pollution emitted from cities has more than just casual stargazers concerned. "Manufacturers are pressuring cities to switch out street lights for LEDs because they save energy," says Susan Harder, New York representative of the International Dark-Sky Association (IDA). But the blue light emitted by LEDs poses risks. It can disrupt circadian rhythms and block the production of melatonin, a known tumor suppressant. It’s also harmful for birds. Guy Maxwell, a partner at Ennead Architects and a champion of bird-safe design, sums it up: "A building that’s fully illuminated, particularly on a night with low cloud cover, confuses them. They end up flying around it in circles until they collapse." The LEED certification system has a light pollution credit, but few regulations are in place. The IDA and others are educating planners on solutions, such as street lamps that direct light downward and scheduling buildings to dim after dark. "A smart city would not just save energy, but use that energy wisely," Harder says.