I have some lights inside the shadows in Three js

Below is my three js code;

const directionalLight = new THREE.DirectionalLight(0xffffff, 1);
directionalLight.position.set(-0.6, 1, 1).normalize();
scene.add(directionalLight);
const backLight = new THREE.DirectionalLight(0xffffff, 1);
backLight.position.set(0.6, -1, -1).normalize();
scene.add(backLight);

This gives me shadow lke this how to fix this but when i remove the backLight it fixes.

Please Help.