PerVertexLighting
http://en.wikibooks.org/wiki/GLSL_Programming/GLUT/Diffuse_Reflection
http://en.wikibooks.org/wiki/GLSL_Programming/GLUT/Specular_Highlights
PerPixelLighting
http://en.wikibooks.org/wiki/GLSL_Programming/GLUT/Smooth_Specular_HighlightsÂ