three.js aomap贴图贴完后为什么会在模型背面显示，模型正面却没有

Question

three.js中使用aomap贴图贴完后为什么会在模型背面显示

var texture = textureLoader.load('model/W_ZYZ_3.jpg');
var textureSpecularQP = textureLoader.load('model/W_XZ01_QP.png');
var materialQP = new THREE.MeshLambertMaterial({
  map: texture,
  color:  0xd4d4d4,
  aoMap: textureSpecularQP, 
  aoMapIntensity  :0.7,
  emissive:0x000000,
  side: THREE.DoubleSide
});

mesh = new THREE.Mesh( geometry, materialQP~~~~ );

但是正面却没有

贴图如下