NEW YORK, July 21 (Reuters) - A coalition of families is asking New York City schools to immediately remove aging fluorescent light fixtures it says are leaking a toxic substance that may harm children's health.

The New York City Department of Education committed in February to replacing the light fixtures over 10 years, but a lawsuit filed by New York Communities for Change on Wednesday in Brooklyn federal court contends that the removal time frame is "unacceptably lax" given the "significant risks" the leaks pose to the health of children in hundreds of schools across the city.

In 2010, a DOE report estimated that 772 city schools were using the light fixtures in question, parts of which contain polychlorinated biphenyl, or PCB, according to court documents. The U.S. Environmental Protection Agency severely restricted the use of PCBs in 1978, declaring them a probable carcinogen linked to developmental disruptions in children.

The DOE report included the results of a pilot study conducted in 2009 showing that the light fixtures were leaking PCB in amounts that were in many cases well over the EPA threshold for PCB air levels in schools, according to the lawsuit. In addition to the light fixtures, PCBs were also identified in caulk used in construction materials for schools.

Given the dangers, the city's 10-year plan to replace the pre-1978, PCB-leaking light fixtures doesn't go fast or far enough, according to Communities for Change, which represents families from low- and moderate-income communities across New York City.

TIME FRAME 'A JOKE'

Experts consulted by the plaintiffs have estimated the replacement plan could be executed in as little as two years, said Miranda Massie, an attorney with New York Lawyers for the Public Interest, which represents the plaintiffs. The savings to the city from replacing the decades-old light fixtures should also help the city in the long run, she added.

"What's absolutely clear is that 10 years is unreasonable and a joke," Massie said.

The plaintiffs are seeking a court order directing the city to commit to a faster time frame for removing and replacing the aging light fixtures. The same group also filed a lawsuit in 2009 seeking removal of the PCB-tainted caulk; that suit was put on hold while the city conducted the pilot study that uncovered the presence of PCB in the lighting.

Natalie Ravitz, a spokeswoman for the DOE, called the city's $708 million plan "unprecedented" compared to other cities experiencing the same issue with PCBs.

"While some people think we should spend more and do this faster, we continue to believe this is an aggressive, environmentally responsible plan that will cause minimum disruption to student learning and generate significant energy savings for the city and taxpayers in the long run," Ravitz said in a statement.

The case is New York Communities for Change v. New York Department of Education et al., in the U.S. District Court for the Eastern District of New York, no. 11-3494.

For New York Communities for Change: Miranda Massie of the New York Lawyers for the Public Interest.

For the DOE: Not immediately available.

(Reporting by Jessica Dye)