The National Library in Singapore is an internationally acclaimed green building that receives 4 million visitors annually. It was designed as an integrated learning center to meet users' needs for connectivity, efficiency, convenience and comfort. Key green features include the use of bioclimatic landscaping to improve indoor climate and a lighting control system that switches off lights when there is sufficient natural light. The library holds events like a book exchange in April 2010 where visitors can exchange used books for new books.