Lighting a Memorial
One of the most compelling renderings of the Pentagon Memorial shows the park at night. The ambience of the place is largely conveyed by the site lighting, which comes from the glowing pools beneath the Memorial Unit seating surfaces. The light reflects off the curve of the cast metal bench and spills onto the surrounding gravel and site features.
The design intent is for the light source to be as crisp and “white” as possible. The effect is meant to be visible to traffic driving along the adjacent roadways as well as planes on the flight path to and from Ronald Reagan National Airport. Because the Memorial Units are laid out chronologically based upon the birth years of the victims, the light patterns will indicate an abstract demographic cross section of the victims, showing the random nature of the September 11, 2001 attack on the Pentagon.
Designers have been exploring solutions to achieve the desired lighting effect throughout the research and development of the Memorial Unit. A thorough investigation of potential light sources has evaluated fiber optics, light emitting diodes (LED), and more conventional incandescent lighting sources. The light source will be housed in a “dry” compartment custom designed into the Memorial Unit pool.
The Lighting Research Center at Rensselaer Polytechnic Institute (RPI) is advising the design team in developing the site lighting. The first phase of this work began last summer, when RPI’s Dr. Yukio Akashi took light level readings to measure the ambient light spilling onto the site from adjacent parking lots, roadways, and buildings. Working with concept designer Julie Beckman and landscape architect Craig Atkins, Dr. Akashi measured horizontal and vertical illuminance distributions between 9 and 11 pm on a typical weeknight. In order to gauge current light levels at the site, and to understand where existing light is coming from, horizontal and vertical measurements facing north, east, south, and west were taken and mapped at each point on a 40’ ? 40’ grid across the future park.
Dr. Akashi found that a relatively uniform light level exists across most of the site, with an exceptionally bright area in the northwest corner, closer to pole-mounted luminaires along the highway. Based upon the level of ambient light today, the Lighting Research Center expects that the average illuminance at the site will reach 2 lux after the memorial and its lighting are installed. This meets the Illuminating Engineering Society of North America’s (IESNA) recommendation for visual performance.
The ultimate selection of a lighting source and design of the Memorial Unit’s “Light Housing Unit” (L-HUB) will proceed based upon these findings and in continued consultation with the Lighting Research Center, the foundry, and the ultimate “operators” of the Memorial at the Pentagon.
The Pentagon maintains a commitment to sustainability in design, so energy conservation and lamp life are significant considerations in the ultimate decision. The top contenders for selection are currently Light Emitting Diodes (LEDs), which offer an estimated life of 70,000 hours, and QL induction lamps, which last 100,000 hours. In addition to benefiting the environment, these light sources will simplify park maintenance by reducing the frequency that lamps will need to be replaced.
Jill Dowling
Design Manager
Centex Lee, LLC