<P> The two beams cost approximately $1,626 (assuming $0.11 per kWh) to run for 24 hours . There are 88 xenon spotlights (44 for each tower) which each consume 7,000 watts . </P> <P> The idea of two vertical beams of light was first suggested by Ezra Orion, an Israeli sculptor, in 1997 . Orion proposed an art installation in which 120 Xenon searchlights were to be placed on the tops of the Twin Towers for the 1998 4th of July celebration . On September 25th, 1997, Orion met with Richard Hart, the president of Xenotech Lighting, and the municipal art adviser, at the top of the south tower . Although the response to Orion's suggestion was enthusiastic, it was deemed too expensive . </P> <P> The Tribute in Light initially ran as a temporary installation from March 11 to April 14, 2002, and ran again on September 11, 2003 to mark the second anniversary of the attack . Since then, it has been repeated every year on September 11 . It was announced that 2008 would be its final year, but the tribute was continued in 2009 . </P> <P> On December 17, 2009, it was confirmed that the tribute would continue through to the tenth anniversary of the attacks in 2011, but continued again in 2012 . As of July 23, 2012, plans are underway for the National September 11 Memorial & Museum to assume the lease for the MTA property used during this tribute, and to begin transitioning operation of the tribute from the Municipal Art Society to the memorial foundation . </P>

When do the twin tower lights come on