Initially, city officials wanted the plaza to meet a minimum of 5 footcandles per square foot. However, after extensive study and site visits to other parks throughout the city, the lighting design team was able to show, based on their collected data, that this amount was excessive and that 0.5 footcandles would provide enough illumination.
The landscape design includes more than 400 white oak trees across the site. Square light columns, each standing just over 16 feet tall, incorporate security cameras and radio antennas along with the lighting element at the top: prismatic refractors with four 4-foot-long T8 lamps.
The two 200-foot-square reflecting pools mark the original footprints of the towers. Each pool features a 30-foot cascading waterfall on every side, illuminated by a custom-designed submersible fixture. A bronze parapet wall inscribed with the names of the victims rings the reflecting pools.
For the parapet lighting, several full-scale working mock-ups helped to determine the positioning between the lamp and the reflector for optimum angle and performance within the specific shape of the parapet enclosure.
One of the project’s technical achievements is the lighting of the waterfalls. The relevant National Electric Code dictated that a submersible fixture run on 25V or less. In 2005, when the project began, the only option for a luminaire of this kind was with low-voltage incandescent or halogen sources. From a long-term maintenance perspective this was not an option.
Instead, the designers, Fisher Marantz Stone, worked closely with Winona Lighting to develop a submersible fixture using LEDs (still an immature technology at the time) that would meet the project’s technical requirements. The result was a 24V-fixture with an internal water-cooling technology. 1,500 linear feet of fixtures are mounted beneath the waterfall at the base of each pool.