heliostat

noun

1. A device that includes a plane mirror which turns so as to keep reflecting sunlight toward a predetermined target, compensating for the sun's apparent motions in the sky. The target may be a physical object, distant from the heliostat, or a direction in space, and is almost always stationary relative to the heliostat, so the light is reflected in a fixed direction.

   “Each heliostat can be directed to bathe a particular park bench or tree in a beam of light. […] The three heliostats cost $355,000 together, not apiece.”

   “In reply, the clockwork heliostats that had tracked the sun to reflect light into the indoor areas during the day now swivelled towards the street lamp to do the same for the night.”