Lighting a world
The reflection and fluorescence caused by sunlight in a daylight scene effectively makes every object a light source. One may use a manageable number of lights if the scene is broken into a number of principle regions. First, there is the disk of the sun. Then there is a pool of extreme brilliance around the sun caused by the scattering effects of the atmosphere. Next there is bluish light from the air, which can be as bright as 20 per cent of the sun light. The horizon can be considered as the accumulation of all light scattered by the lower atmosphere and objects projecting up from the ground. The ground itself colors and returns a large percentage of incident light. This grouping yields five different kinds of lights.
Consider building a world light set in the following manner. Place an axis at the world origin. This will be used as the parent of a group. Give it an appropriate name, such as "center" or "focus". To facilitate placement, make a sphere with a radius of 512 units, 36 circle sections and 18 vertical section.
The following light axes will be placed around the edge of this. All lights will be grouped to the center. Depending on the size of the world to be illuminated, this group can simply be scaled up or down.
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