Final answer:
Phillip K. Smith III adds mirrors and lights to create an illusion of disappearing walls and allow brilliant, luminous colors into the space.
Step-by-step explanation:
Phillip K. Smith III adds mirrors and lights to an old shack in Lucid Stead for two main reasons: engineering the structure to create an illusion of disappearing walls and replacing them with colored glass to allow brilliant, luminous colors into the space. By adding mirrors and lights, Smith transforms the shack into a visually stunning and immersive installation that plays with reflections and perception.