Lightfall

The Light Cannon is a custom built optical machine mounted on the roof of a 16 story building that tracks the sun by movement on two axes. The front window is made out of floated borosilicate glass that filters out infrared and ultraviolet wavelengths. The mirrors inside the Cannon collect, concentrate and redirect visible solar radiation through the shaft below into the Redirecting Optics. The shape of the Cannon was designed to reduce windage for the instrument. Under high wind conditions the instrument is programmed to stop tracking and park itself to avoid excessive loads.

The Redirecting Optics consist of a series of mirrors and lenses that provide a pathway for the light to travel from the Light Cannon, around the mechanical equipment on the 16th and 17th floors, and into the top of the stairwell, terminating on a truss suspended above the Light Dagger. A second set of optics inhabiting the same light shaft provides the real time white light image of the solar disc on the ceiling of the stair.

Structurally, the dagger is supported by four tensioned steel cables that span the full height of the stair from the floor to ceiling. From these cables are hung 16 stainless steel rings, spaced 15’ apart. The Dagger itself is tapered in shape, so the top ring is the largest with an interior diameter of 24,” and at the bottom ring the outside diameter is less than 10”. Each ring acts as a connection point and interface for all the optical components of the Light Dagger.

Between rings, the light beam is visible through the hanging fibers as it travels down to the first floor. At night, or on a cloudy day, the dagger appears almost like a fluted column, with a series of tall white round fibers creating this effect. When the sun is out, the sculpture becomes bright, providing both light and a connection to the sky.
Varying levels of glowing light emit from the sides of the fibers, with bright spots of light interspersed, highlighting the ends of each individual fiber.

Side-by-side falsecolor comparison perspective view of Light Dagger showing the surface brightness (luminance) for both simulated (left) and completed building (right). During the design phase of the project, we used photometrically accurate ray-tracing software (Radiance) and created high dynamic range (HDR) renderings of the light sculpture in context with the proposed stairwell. The simulation included the proposed electric lighting scheme using manufacturer’s IES photometric files as input for each of the luminaires. The image on the right is a real photograph of the finished sculpture taken with a calibrated camera and post-processed to the same brightness scale as the simulation. The input for the simulation was derived by measuring a full scale mockup of the fiber bundles that we setup in our lab. The simulation turned out to be conservative as we had assumed higher light losses in the optical train, and therefore the sculpture resulted in being brighter than anticipated.