What:
"Shadow Walk" is part of the Mesa Arts Center and a place where the rich interplay of overlapping shadows, trees and architectural canopies create a cool and inviting environment. Long, curving lines of trees, shift back and forth as one walks along the promenade, throwing different shadow forms on the ground and creating different qualities and quantities of shadow. In addition to shadows thrown by vegetation, a series of colored glass canopies and raised glass screens will cast colored shadows on the ground.
So What:
Use of shadows as part of the art work---ephemeral and always changing
Use of reflective materials such as glass and mirror
Art work has functionality in that it creates shade

http://www.marthaschwartz.com/prjts/commercial/mesa/mesa.html