So this abandoned? feature of three.js seems to have become somewhat of a holy grail; I've tried to implement it a couple of times unsuccessfully.
The example working on an old release is here: https://threejs.org/examples/#webgl_lights_rectarealight
My minimal broken example is here: https://jsfiddle.net/bitsofcoad/1k3arL33/
var width = 20;
var height = 20;
var rectLight = new THREE.RectAreaLight( 0xffffff, 500, width, height );
rectLight.intensity = 500.0;
rectLight.position.set( 0, 30, 0 );
rectLight.lookAt( mesh2.position );
scene.add( rectLight )
var rectLightHelper = new THREE.RectAreaLightHelper( rectLight );
scene.add( rectLightHelper );
I have made sure to include the proper rectarealight library in the jsfiddle.
This thread was particularly enlightening on the topic of why this PR had some difficulties: https://github.com/mrdoob/three.js/pull/9234
And this thread was interesting to see how far other people had gotten in developing a similar type of light for three.js:
Improved Area Lighting in WebGL & ThreeJS
I don't really know what happened to break abelnation's example, or even if it is completely broken ( I may have screwed up my jsfiddle... ), but I think there is still considerable interest in this feature.
The soft edges look so nice, I'm tempted to cannibalize WestLangley's custom shader (http://jsfiddle.net/hh74z2ft/89/), which has pretty much all the functionality I need.
Anybody else able to get the basic functions working? Thanks!