Default GL_LIGHT_MODEL_AMBIENT equals to {0.2f, 0.2f, 0.2f, 1.0f} and it affects to light equation calculation more than
 it must affect. For example if GL_LIGHT_MODEL_AMBIENT equals to {1.0f, 1.0f, 1.0f, 1.0f} I will get maximum bright 
color without any shadings, but look into the color computation equation when lighting is enabled, you'll see that 
GL_LIGHT_MODEL_AMBIENT must not affect so dramatic to the result color.

The same behavior using software renderer and hardware renderer provided by devg-extreme2.