title: Why GL_SPECULAR doesn't work?
body: <p>I've downloaded the code from NeHe tutorial, the one about lighting. The original code didn't include  the specular light, I simply added it. I defined a free color-lighting arrays and shut out the other lights.</p>
  
  <pre><code>GLfloat LightBlack[] = { 0.0f, 0.0f, 0.0f, 1.0f };
  GLfloat LightGreen[] = { 0.0f, 1.0f, 0.0f, 1.0f };
  
  ...
  
  glLightfv(GL_LIGHT1, GL_AMBIENT, LightBlack);       // add lighting. (ambient)
  glLightfv(GL_LIGHT1, GL_SPECULAR, LightGreen);      // THIS IS WHAT I ADDED
  glLightfv(GL_LIGHT1, GL_DIFFUSE, LightBlack);       // add lighting. (diffuse).
  glLightfv(GL_LIGHT1, GL_POSITION, LightPosition);   // set light position.
  
  ...
  
  glutSolidTeapot(0.8f);
  </code></pre>
  
  <p>However, the result seemed that all the lights are shut, there are no lights at all. Seems that the GL_SPECULAR didn't work. Why is that?</p>
  
  <p>With glDisable(GL_LIGHTING);
  <img src="https://i.stack.imgur.com/QH6nh.png" alt="With glDisable(GL_LIGHTING);"></p>
  
  <p>With glDisable(GL_LIGHTING);
  <img src="https://i.stack.imgur.com/Iq03a.png" alt="With glEnable(GL_LIGHTING);"></p>