# point light shining "through" polygons?

How can I get the point light to stop shining through the polygons? Faces that should be occluded by other faces are glowing green... :(

TestGrid = Table[0, {i, 5}, {j, 5}];
DrawCubby[color_, position_] :=
{Polygon[{{position[[2]] - 1, 0, position[[1]] - 1}, {position[[2]],
0, position[[1]] - 1}, {position[[2]], 0,
position[[1]]}, {position[[2]] - 1, 0,
position[[1]]}, {position[[2]] - 1, 0, position[[1]]}}],
Polygon[{{position[[2]] - 1, 0,
position[[1]] - 1}, {position[[2]] - 1, 1,
position[[1]] - 1}, {position[[2]], 1,
position[[1]] - 1}, {position[[2]], 0,
position[[1]] - 1}, {position[[2]] - 1, 0, position[[1]] - 1}}],
Polygon[{{position[[2]] - 1, 0,
position[[1]] - 1}, {position[[2]] - 1, 1,
position[[1]] - 1}, {position[[2]] - 1, 1,
position[[1]]}, {position[[2]] - 1, 0,
position[[1]]}, {position[[2]] - 1, 0, position[[1]] - 1}}],
Polygon[{{position[[2]] - 1, 0, position[[1]]}, {position[[2]] - 1,
1, position[[1]]}, {position[[2]], 1,
position[[1]]}, {position[[2]], 0,
position[[1]]}, {position[[2]] - 1, 0, position[[1]]}}],
Polygon[{{position[[2]], 0, position[[1]] - 1}, {position[[2]], 1,
position[[1]] - 1}, {position[[2]], 1,
position[[1]]}, {position[[2]], 0,
position[[1]]}, {position[[2]], 0, position[[1]] - 1}}]
};
Manipulate[
Graphics3D[{Lighting -> {{"Point", Green, {a, b, c}, {0, 1, 0}}},
MapIndexed[DrawCubby, TestGrid, {2}], PointSize[Large], Pink,
Point[{a, b, c}]}], {{a, .5}, 0, 2}, {{b, .5}, 0, 2}, {{c, .5}, 0,
2}]