This command sets the diffuse component of the current surface lighting properties. The diffuse component specifies how much the world's directional light source "shines" on polygons. It also specifies how much individual light sources placed within the world shine on the polygons. It should be specified in the range 0.0 to 1.0. A light source shines more brightly on polygons facing the light source. It does not shine at all on polygons that face away from the light source.
<diffuse> the diffuse lighting value to set