Thanks for explanations. I agree that in general those lines of the code are not equivalent (for example light_view_matrix may contain some rotation)
But in this particular case the light_view_matrix contains only a translation:
glLoadIdentity(); glTranslatef(-light_position_ws, -light_position_ws, -light_position_ws); glGetFloatv(GL_MODELVIEW_MATRIX, light_view_matrix);
The light_view_matrix looks like this:
1 0 0 0 0 1 0 0 0 0 1 0 -light_posX -light_posY -light_posZ 1
So those lines of code give me the same result when I run the program. If I'm still wrong please give some example.