title: Lights on BufferGeometry not correct
body: <p>I got a BufferGeometry that uses MeshLambertMaterial and VertexColors. When I apply lights as the gif below shows, the lights gets distorted when the BufferGeometry consists of different sizes of faces with the same color. If I use different colors for each face with smaller faces (1x1) the lights looks good. I've tried to calculate faceNormals but that doesn't solve the issue. </p>
  
  <p>Anything I miss?</p>
  
  <p><a href="https://media.giphy.com/media/xUA7aO4fMOaOBeVB60/giphy.gif" rel="nofollow noreferrer">Here is a gif showing the issue</a></p>