Terragen's Sunlight node emits light in parallel rays.
By changing the Sunlight node's Heading and Elevation settings you can change the direction of illumination. In the first example image below, the Heading values of 0, 90, 180, or 270 degrees correspond to North, East, South and West illumination, and the Elevation values of +90 or -90 correspond to top and bottom lighting.
In the second example image, six Sunlight nodes are added to the project, each one corresponding to North, East, South, West, Top, and Bottom. Each Strength setting = 1, and the Bottom Sunlight node's Cast Shadows option is off.
For more information on the Sunlight node, check out the Wiki documentation here:
https://planetside.co.uk/wiki/index.php?title=Sunlight