A sunny morning at the new Haus der Forschung in Vienna brings more than another day’s work. Through a system of mirrors, prisms, and fiber cables, sunlight itself is funneled into the foyer. Snaking through the Forschung ceiling is the latest experiment in heliostatic lighting—bringing the sun inside the building.

Heliostats are mirror arrays that track the sun, following preprogrammed sequencing directions from software or responding to exterior-mounted sensors. Sunlight can be reflected from a large, high-quality, žroof-mounted circular tracking mirror to a secondary mirror or mirrors, and then directed inside a building, letting sunshine appear as if it were provided by electrical sources.