public void setLightDirection(Vector3f lightDirection) {
        this.lightDirection = lightDirection;
        if (material != null) {
            material.setVector3("LightDir", lightDirection);
        }
    }
Sets the light direction

@param lightDirection the direction vector to use (alias created,
default=(0,-1,0))
jme3-effects/src/main/java/com/jme3/water/WaterFilter.java