@Override
    public void read(JmeImporter im) throws IOException {
        super.read(im);
        InputCapsule ic = im.getCapsule(this);
        position = (Vector3f) ic.readSavable("position", null);
        radius = ic.readFloat("radius", 0f);
        if (radius!=0) {
            this.invRadius = 1 / radius;
        } else {
            this.invRadius = 0;
        }
    }
for internal use only
@return the inverse of the radius
jme3-core/src/main/java/com/jme3/light/PointLight.java