102 LIGHT + TECH


AN INGENIOUS conjunction of light art, science and multi-purpose monument, the Arco del Tiempo (Arch of Time) has been hailed as setting a new standard of sustainability for public art. Scheduled to be installed in 2024, the striking sculpture is a solar power generator that provides a shaded place to ‘meet, linger, experience


and perform’. Located in Houston’s Guadalupe Plaza Park, the 30m-high arch will serve as a landmark and gateway to the Texan city’s East End/Segundo Barrio. But it is also one of the world’s largest sundials, an interactive time-measuring device that operates by beaming sunlight onto the ground through the solar-shaped


holes in the roof of the structure. Each beam of light is uniquely governed throughout the seasons and hours of the day by the geometry of the artwork, responding to the specific latitude and longitude of Houston.


This mechanism also creates a playful hourly light display that the public can


HOW IT WORKS


The design of the artwork is inspired by the sundial – the oldest known device used to measure time based on the sun’s apparent position in the sky. The artwork deviates from the typical sundial configuration by reversing the role of the gnomon, which traditionally casts shadows. Instead, the time of day is indicated by sunlight projected onto the ground through a series of openings on the surface facing south. This surface is also covered with


photovoltaic modules which generate renewable energy.


The sculpture’s shape is defined by the diurnal motion of the sun in the Houston sky throughout the year. The path that the sun traces in the sky has been enlarged around noon and tapered at sunrise and sunset. This configuration optimises the exposure of the photovoltaic cell surface by increasing it during the peak sun hours.


The operating principle of the artwork involves displaying diff erent hours through sunlight cast in the form of abstract symbols representing the face of a


clock. Solar noon is depicted by a full circle of sunlight projected on to the ground. The hours before and after solar noon are represented by a growing circular sector within the circle, extending towards sunrise and sunset. To diff erentiate between the hours, various shades of colour are used, reminiscent of both the sky and various portrayals of Our Lady of Guadalupe (associated with the story of a series of apparitions of the Virgin Mary to a Mexican peasant in 1531). Coloured glass


This image The Arco del Tiempo’s design plans, showing how the


artwork takes advantage of the movement of the sun to tell the time and to generate clean, renewable solar energy


filters, ranging from pink in the morning to blue in the evening, filter the sunlight to create the eff ect. In the north/south section, the shape of the openings is defined by the solar declination, covering the angles of the summer and winter solstices. The equinox line is perpendicular to the photovoltaic surface. The openings indicating the time are shorter than the parallel louvres, allowing the sun’s rays to illuminate the hours at all angles of incidence from solstice to solstice.


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