The heliodon is a device that, together with a customized sundial and an angle of incidence indicator, can be used by an architect, landscaper, homeowner, or solar energy technician to visualize the way solar energy affects structures at any time of any day of the year.

The picture below shows a model of a building at latitude 42° North oriented toward a light source as it would be oriented toward the sun at 10:30 a.m. on the winter solstice. This is the shortest day of the year, when the sun is lowest in the sky. The rectangular object in the foreground is the sundial, and the round object beside the house is the angle of incidence indicator. Click on these for a larger picture and more information.