The Manhattan skyline — glimmering, grand but not always environmentally efficient — may need to go darker to go green.  Amid a far-reaching push to reduce New York’s environmental footprint, city officials on Wednesday weighed a City Council bill to limit internal and external light use in many commercial buildings when empty at night, a change that could affect some 40,000 structures and rethink the shape, or at least the hue, of what residents see when they look up.  The environmental considerations are clear: reducing potentially wasteful energy use as part of the city’s bid to curb its greenhouse gas emissions. The administration of Mayor Bill de Blasio has expressed support for passing a version of the bill, calling light pollution a citywide scourge for migratory birds and sedentary New Yorkers.  The hearing, accordingly, cast a wide net, touching on amphibious mating activity, the astrophysicist Neil deGrasse Tyson and even the very definition of nighttime. And it hinted at a host of complications in the proposed legislation, among them an exception for buildings found to be “a significant part of the city’s skyline.”  City officials expressed misgivings about playing favorites with cherished destinations, potentially empowering government workers to decide which structures were notable enough to stay lit.  “The mandate to curate, if you will, the skyline of the city of New York is not something the commission does currently,” said Mark Silberman, general counsel for the city’s Landmarks Preservation Commission.  The proposal, he added, “does put the commission in a slightly uncomfortable position, perhaps, of choosing between landmarks.”  Councilman Donovan Richards Jr., the bill’s lead sponsor, joked that the change would “add excitement” to the lives of city regulators.  “We’re not looking for excitement,” Mr. Silberman said.  Some critics, including food industry and real estate leaders, worried that reduced lighting could affect safety.  “Security cameras would be useless in the dark, and police officers would no longer peek into darkened stores at night,” said Jay M. Peltz, general counsel for the Food Industry Alliance of New York State.  Administration officials said they shared concerns about maintaining adequate lighting to deter crime, suggesting that they would move to tweak the bill. It was not immediately clear how.  The bill does exempt buildings “where individuals are inside” at night, which would seem to apply to the many large office buildings that maintain a limited security presence or bring in cleaners overnight.  Other exemptions in the bill include a provision allowing “temporary seasonal displays” to remain illuminated in storefront windows.  Offending building operators could be fined $1,000 for violating the lighting standards, according to the bill.  A few advocates said the bill was not strong enough, wondering if skyscrapers like the Empire State Building really needed to stay bright all night. (Officials suggested that the Empire State Building and Chrysler Building, among several others, would appear likely candidates for an exemption.)  “Many of us have felt a sense of pride in its beauty,” one public speaker, Catherine Skopic, said of the skyline. “However, now that we are in this climate crisis, we see these lights as something else. We see them as wasteful of energy.”  The Real Estate Board of New York, which opposes the bill as written but says it shares many of its goals, argued that energy code changes had already ensured improved efficiency standards for skyscrapers in the coming years.  At times, the hearing veered into the stuff of middle school science textbooks — “animal activities that are regulated by the length of day include migration, hibernation and procreation,” Mr. Richards reported during an extended lament on light pollution’s effect on wildlife.  Artificial light can deter nesting female sea turtles, Mr. Richards noted, and interfere with the habits of hatchlings. Monarch butterflies grow disoriented. Male blackbirds fail to develop reproductive organs.  “Frogs stopped mating activity,” Mr. Richards said grimly at one point, “during night football games when lights from a nearby stadium increased sky glow.”  The hearing included a call-in from a former French environment minister, who required an in-house translator. Preliminary data, Mr. Richards said, showed a 9 percent reduction in energy use in France as a result of changes akin to his proposal.  Mr. Richards, a Queens Democrat, had seen the fruits of the French effort during a recent visit, he said, casting himself as an atypical tourist in the City of Light — the traveler eager to see less of it. “I traveled to Paris last year,” he said, “and I got to see lights off myself.”  A version of this article appears in print on April 30, 2015, on page A23 of the New York edition with the headline: City May Dim the Lights to Aid the Environment. Order Reprints| Today's Paper|Subscribe
Mayor Bill de Blasio’s administration and a host of environmental advocates agree that light pollution should be addressed, but some are disputing parts of a proposed City Council bill.