lighting in tesselated polygons

I have drawn a concave polygon using tesselation functions. When I draw the object CCW (as expected) and give the polygon normal as (0,0,1), it makes the lighting calculations correct.
However, I want to light the other side of the polygon. For this reason, I changed the order of vertices (to make the polygon in CCW order whwn looking at other side) and changed the normal as (0,0,-1). However, the lighting is not correctly done for the otherside of the polygon, and it becomes black. The code is below, can anyone describe me where I am doing wrong?

gluTessBeginPolygon(tobj, NULL);
gluTessVertex(tobj, dummy1[0], dummy1[0]);
gluTessVertex(tobj, dummy1[3], dummy1[3]);
gluTessVertex(tobj, dummy1[2], dummy1[2]);
gluTessVertex(tobj, dummy1[1], dummy1[1]);

The glLightModel call may help you out:

You can just enable two sided lighting.