Would a SunAngle sysvar be useful? Bots could roughly navigate with it.
As Eric briefly pointed out, alot of this depends on what we take the field to be. Is it part of a larger planet, and so has dawn/noon/dusk? Is it an entire (small) planet, with parts in light and others in darkness? Or is it a pitri dish with a relatively close lightbulb?
Each answer gives different possibilities for navigating with the sun.
