Is there a rule-of-thumb I should follow when using some of the Paint Brush Load parameters?
Specifically, under what conditions are the 3D Lighting and Shadow Lighting parameters effective? It appears one cannot simply choose a random brush and then make it appear to have some sort of 3D characteristic simply by choosing 3D Lighting and/or Shadow Lighting. What other properties must a brush have before one may use those parameters?
Well, it has to be a raster paint effect. Brush Load is a raster image processing module in the paint synthesizer. If it's pure vector, then paint Brush Load control panel isn't doing anything to affect the vector paint.
And of course you need to be using Brush Load in the Paint Fill Setup control panel.
If you have a pure vector paint effect, then you need to use the appropriate vector shadowing controls.
If you have any questions about specific presets, fire away and i'll try to answer.