Check this blend file and notice that Pot 1 is in layer 1, as is the sun, whose light is set to “This Layer Only”. Thus Pot one appears lit in the editor, and Pot 2 who is in layer 2 is dark as you’d expect.
However, hit “P” to run the game engine, and notice how Pot 1 goes black too. Now change the sun to the same layer as Pot 2 and run it again, and notice they both light up, even though Pot 1 is in a different layer.
Thus It seems that in the BGE, Pot 1’s layer is ignored, and Pot 2 alone is deciding the layer of pot 1 for lighting. It’s like they’re still linked or something, but I believe I created Pot 2 by duplicating with Shift-D, not Alt-D, so they should be separate data blocks - right?
I’ve bumped into this issue a number of times in the BGE after hours of debugging, yet duplicating the default cube and lamp in the factory settings doesn’t reproduce the issue, so I’ve either found a bug in the BGE or have something to learn about of duplicated objects.