A study of the capacity of nightclubs to convert to environmentally sustainable practices, the Sustainable Dance Club uses a system of floor tiles that generate energy when compressed to power lights and sound systems. The concept was first tested with over 1,200 dancers at the Rotterdam club Off-Corso, and has since developed into a system of standards for limiting environmental impact and communicating sustainable design to the public. Club Watt, also in Rotterdam, became the first club to earn the Sustainable Dance Club label on a permanent basis in September of 2008. Sustainable Dance Club is a collaboration between Enviu and Döllab, which began in 2005.  Enviu is an international network for young entrepreneurs interested in sustainability. Döllab is a Dutch architectural firm based in Rotterdam and founded in 2003 by Henk Döll.