When a room has just one window heading toward north, it never receives direct sun light, causing people to keep lights turned on during daytime.
An heliostat costantly follows the Sun while it moves in the sky, reflecting its light to a fixed position, like a window (or a solar panel).
Commercial heliostats are huge and expensive.
This one is based on just a standard ipCam priced 30-40$ connected to a PC, and an old CD glued to it used as a mirror. It is remotely operated by a javascript program running on a PC, which makes the camera move according to sun position astronomic calculation with no need for light sensors. It keeps working when cloudy, getting immediately back to work as soon as Sun is visible again, never losing tracking.
Next step in desing will be controlling the camera by a RaspberryPI rather than a PC, to make it standalone.