Michael Dumiak in the Architectural Record:
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.
The mirrors have been around for decades. However, only recently, with increased interest in green energy and CNC cutting processes, which have reduced the costs of machining specialty optics, have architects begun to seriously consider using the mirrors for light and energy sources.
More here. [Incidentally, I thought of the same idea to pipe sunlight from the roof of my building into my too-dark apartment last year, and even researched the prices of fiber optic cable bundles, but abandoned the project after calculating that the concentrated sunlight would melt the cables–I couldn’t afford too large a bundle–and be a fire hazard.]