To address direct sunlight related issues, such as solar heating, glare, overshading; the sunlight's beam must be controlled. Since the sun's position fluctuates with time, the phenomenon must be simulated over time.

Spot is a Java3D applet tool aimed at helping architects quickly visualize the amount of direct sunlight that reaches specific areas over time. To find the opportunities to use (or avoid) direct day lighting over a period of time, for example from 8AM to 4PM during November-February, Spot displays sunlight distribution over the space in a navigable virtual 3D world. The distribution of light over time for a given point is displayed in additional views that are calendars.

The current version of Spot in implemented in SpacePen (by Thomas Jung, Ellen-Do, Mark Gross-DMG), a project aimed at annotating 3D models.