Nevertheless, New York faces growing energy demands and limited space. The city has introduced a series of environmental policies since the 1990s to address these problems. Detailed measures included switching more than 11,000 traffic lights and pedestrian signals in the city to new energy-efficient light-emitting diodes that use 90% less energy than conventional fixtures. The city replaced 149,000 "cobra head" street lights with new energy-efficient designs by 2008. Over 180,000 inefficient refrigerators in public housing projects have been replaced with new ones that use a quarter of the power of the old ones. By law, the city government can purchase only the most efficient cars, air-conditioners and copy machines. The electricity used to power the Statue of Liberty, Ellis Island and 22 other federal buildings in New York City, an annual electricity demand of roughly 27 million kilowatt hours, is provided by wind power.