three.js/src/extras/helpers/HemisphereLightHelper.js

/**
 * @author alteredq / http://alteredqualia.com/
 * @author mrdoob / http://mrdoob.com/
 */

THREE.HemisphereLightHelper = function ( light, sphereSize, arrowLength, domeSize ) {

	THREE.Object3D.call( this );

	this.light = light;
	this.light.updateMatrixWorld();

	this.matrixWorld = light.matrixWorld;
	this.matrixAutoUpdate = false;

	this.colors = [ new THREE.Color(), new THREE.Color() ];

	var geometry = new THREE.SphereGeometry( sphereSize, 4, 2 );
	geometry.applyMatrix( new THREE.Matrix4().makeRotationX( - Math.PI / 2 ) );

	for ( var i = 0, il = 8; i < il; i ++ ) {

		geometry.faces[ i ].color = this.colors[ i < 4 ? 0 : 1 ];

	}

	var material = new THREE.MeshBasicMaterial( { vertexColors: THREE.FaceColors, wireframe: true } );

	this.lightSphere = new THREE.Mesh( geometry, material );
	this.add( this.lightSphere );

	this.update();

};

THREE.HemisphereLightHelper.prototype = Object.create( THREE.Object3D.prototype );

THREE.HemisphereLightHelper.prototype.dispose = function () {
	this.lightSphere.geometry.dispose();
	this.lightSphere.material.dispose();
};

THREE.HemisphereLightHelper.prototype.update = function () {

	var vector = new THREE.Vector3();

	return function () {

		this.colors[ 0 ].copy( this.light.color ).multiplyScalar( this.light.intensity );
		this.colors[ 1 ].copy( this.light.groundColor ).multiplyScalar( this.light.intensity );

		this.lightSphere.lookAt( vector.getPositionFromMatrix( this.light.matrixWorld ).negate() );
		this.lightSphere.geometry.colorsNeedUpdate = true;

	}

}();