public void toggleLighting(
    Model lightsModel, boolean lit, float xoff, float yoff, float zoff
  ) {
    if (! lit) {
      if (lightingFX != null) detach(lightingFX) ;
      lightingFX = null ;
    }
    else {
      ///I.say("Toggling lighting on...") ;
      if (lightingFX != null && lightingFX.model() != lightsModel) {
        detach(lightingFX) ;
        lightingFX = null ;
      }
      if (lightingFX == null) {
        lightingFX = lightsModel.makeSprite() ;
        lightingFX.colour = Colour.LIGHT ;
        attach(lightingFX, xoff, yoff, zoff) ;
      }
      else {
        //  TODO:  Vary the intensity of the transparency.
      }
    }
  }