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Three.js Lights

This article is part of a series of articles about three.js. The first article is three.js fundamentals. If you haven't read that yet and you're new to three.js you might want to consider starting there. The previous article was about textures.

Let's go over how to use the various kinds of lights in three.

Starting with one of our previous samples let's update the camera. We'll set the field of view to 45 degrees, the far plane to 100 units, and we'll move the camera 10 units up and 20 units back from the origin

*const fov = 45;
const aspect = 2;  // the canvas default
const near = 0.1;
*const far = 100;
const camera = new THREE.PerspectiveCamera(fov, aspect, near, far);
+camera.position.set(0, 10, 20);

Next let's add OrbitControls. OrbitControls let the user spin or orbit the camera around some point. The OrbitControls are an optional feature of three.js so first we need to include them in our page

import * as THREE from './resources/three/r110/build/three.module.js';
+import {OrbitControls} from './resources/threejs/r110/examples/jsm/controls/OrbitControls.js';

Then we can use them. We pass the OrbitControls a camera to control and the DOM element to use to get input events

const controls = new OrbitControls(camera, canvas);
controls.target.set(0, 5, 0);
controls.update();

We also set the target to orbit around to 5 units above the origin and then call controls.update so the controls will use the new target.

Next up let's make some things to light up. First we'll make ground plane. We'll apply a tiny 2x2 pixel checkerboard texture that looks like this

First we load the texture, set it to repeating, set the filtering to nearest, and set how many times we want it to repeat. Since the texture is a 2x2 pixel checkerboard, by repeating and setting the repeat to half the size of the plane each check on the checkerboard will be exactly 1 unit large;

const planeSize = 40;

const loader = new THREE.TextureLoader();
const texture = loader.load('resources/images/checker.png');
texture.wrapS = THREE.RepeatWrapping;
texture.wrapT = THREE.RepeatWrapping;
texture.magFilter = THREE.NearestFilter;
const repeats = planeSize / 2;
texture.repeat.set(repeats, repeats);

We then make a plane geometry, a material for the plane, and a mesh to insert it in the scene. Planes default to being in the XY plane but the ground is in the XZ plane so we rotate it.

const planeGeo = new THREE.PlaneBufferGeometry(planeSize, planeSize);
const planeMat = new THREE.MeshPhongMaterial({
  map: texture,
  side: THREE.DoubleSide,
});
const mesh = new THREE.Mesh(planeGeo, planeMat);
mesh.rotation.x = Math.PI * -.5;
scene.add(mesh);

Let's add a cube and a sphere so we have 3 things to light including the plane

{
  const cubeSize = 4;
  const cubeGeo = new THREE.BoxBufferGeometry(cubeSize, cubeSize, cubeSize);
  const cubeMat = new THREE.MeshPhongMaterial({color: '#8AC'});
  const mesh = new THREE.Mesh(cubeGeo, cubeMat);
  mesh.position.set(cubeSize + 1, cubeSize / 2, 0);
  scene.add(mesh);
}
{
  const sphereRadius = 3;
  const sphereWidthDivisions = 32;
  const sphereHeightDivisions = 16;
  const sphereGeo = new THREE.SphereBufferGeometry(sphereRadius, sphereWidthDivisions, sphereHeightDivisions);
  const sphereMat = new THREE.MeshPhongMaterial({color: '#CA8'});
  const mesh = new THREE.Mesh(sphereGeo, sphereMat);
  mesh.position.set(-sphereRadius - 1, sphereRadius + 2, 0);
  scene.add(mesh);
}

Now that we have a scene to light up let's add lights!

AmbientLight

First let's make an AmbientLight

const color = 0xFFFFFF;
const intensity = 1;
const light = new THREE.AmbientLight(color, intensity);
scene.add(light);

Let's also make it so we can adjust the light's parameters. We'll use dat.GUI again. To be able to adjust the color via dat.GUI we need a small helper that presents a property to dat.GUI that looks like a CSS hex color string (eg: #FF8844). Our helper will get the color from a named property, convert it to a hex string to offer to dat.GUI. When dat.GUI tries to set the helper's property we'll assign the result back to the light's color.

Here's the helper:

class ColorGUIHelper {
  constructor(object, prop) {
    this.object = object;
    this.prop = prop;
  }
  get value() {
    return `#${this.object[this.prop].getHexString()}`;
  }
  set value(hexString) {
    this.object[this.prop].set(hexString);
  }
}

And here's our code setting up dat.GUI

const gui = new GUI();
gui.addColor(new ColorGUIHelper(light, 'color'), 'value').name('color');
gui.add(light, 'intensity', 0, 2, 0.01);

And here's the result

Click and drag in the scene to orbit the camera.

Notice there is no definition. The shapes are flat. The AmbientLight effectively just multiplies the material's color by the light's color times the intensity.

color = materialColor * light.color * light.intensity;

That's it. It has no direction. This style of ambient lighting is actually not all that useful as lighting as it's 100% even so other than changing the color of everything in the scene it doesn't look much like lighting. What it does help with is making the darks not too dark.

HemisphereLight

Let's switch the code to a HemisphereLight. A HemisphereLight takes a sky color and a ground color and just multiplies the material's color between those 2 colors—the sky color if the surface of the object is pointing up and the ground color if the surface of the object is pointing down.

Here's the new code

-const color = 0xFFFFFF;
+const skyColor = 0xB1E1FF;  // light blue
+const groundColor = 0xB97A20;  // brownish orange
const intensity = 1;
-const light = new THREE.AmbientLight(color, intensity);
+const light = new THREE.HemisphereLight(skyColor, groundColor, intensity);
scene.add(light);

Let's also update the dat.GUI code to edit both colors

const gui = new GUI();
-gui.addColor(new ColorGUIHelper(light, 'color'), 'value').name('color');
+gui.addColor(new ColorGUIHelper(light, 'color'), 'value').name('skyColor');
+gui.addColor(new ColorGUIHelper(light, 'groundColor'), 'value').name('groundColor');
gui.add(light, 'intensity', 0, 2, 0.01);

The result:

Notice again there is almost no definition, everything looks kind of flat. The HemisphereLight used in combination with another light can help give a nice kind of influence of the color of the sky and ground. In that way it's best used in combination with some other light or a substitute for an AmbientLight.

DirectionalLight

Let's switch the code to a DirectionalLight. A DirectionalLight is often used to represent the sun.

const color = 0xFFFFFF;
const intensity = 1;
const light = new THREE.DirectionalLight(color, intensity);
light.position.set(0, 10, 0);
light.target.position.set(-5, 0, 0);
scene.add(light);
scene.add(light.target);

Notice that we had to add the light and the light.target to the scene. A three.js DirectionalLight will shine in the direction of its target.

Let's make it so we can move the target by adding it to our GUI.

const gui = new GUI();
gui.addColor(new ColorGUIHelper(light, 'color'), 'value').name('color');
gui.add(light, 'intensity', 0, 2, 0.01);
gui.add(light.target.position, 'x', -10, 10);
gui.add(light.target.position, 'z', -10, 10);
gui.add(light.target.position, 'y', 0, 10);

It's kind of hard to see what's going on. Three.js has a bunch of helper objects we can add to our scene to help visualize invisible parts of a scene. In this case we'll use the DirectionalLightHelper which will draw a plane, to represent the light, and a line from the light to the target. We just pass it the light and add it to the scene.

const helper = new THREE.DirectionalLightHelper(light);
scene.add(helper);

While we're at it let's make it so we can set both the position of the light and the target. To do this we'll make a function that given a Vector3 will adjust its x, y, and z properties using dat.GUI.

function makeXYZGUI(gui, vector3, name, onChangeFn) {
  const folder = gui.addFolder(name);
  folder.add(vector3, 'x', -10, 10).onChange(onChangeFn);
  folder.add(vector3, 'y', 0, 10).onChange(onChangeFn);
  folder.add(vector3, 'z', -10, 10).onChange(onChangeFn);
  folder.open();
}

Note that we need to call the helper's update function anytime we change something so the helper knows to update itself. As such we pass in an onChangeFn function to get called anytime dat.GUI updates a value.

Then we can use that for both the light's position and the target's position like this

+function updateLight{
+  light.target.updateMatrixWorld();
+  helper.update();
+}
+updateLight();

const gui = new GUI();
gui.addColor(new ColorGUIHelper(light, 'color'), 'value').name('color');
gui.add(light, 'intensity', 0, 2, 0.01);

+makeXYZGUI(gui, light.position, 'position', updateLight);
+makeXYZGUI(gui, light.target.position, 'target', updateLight);

Now we can move the light, and its target

Orbit the camera and it gets easier to see. The plane represents a DirectionalLight because a directional light computes light coming in one direction. There is no point the light comes from, it's an infinite plane of light shooting out parallel rays of light.

PointLight

A PointLight is a light that sits at a point and shoots light in all directions from that point. Let's change the code.

const color = 0xFFFFFF;
const intensity = 1;
-const light = new THREE.DirectionalLight(color, intensity);
+const light = new THREE.PointLight(color, intensity);
light.position.set(0, 10, 0);
-light.target.position.set(-5, 0, 0);
scene.add(light);
-scene.add(light.target);

Let's also switch to a PointLightHelper

-const helper = new THREE.DirectionalLightHelper(light);
+const helper = new THREE.PointLightHelper(light);
scene.add(helper);

and as there is no target the onChange function can be simpler.

function updateLight{
-  light.target.updateMatrixWorld();
  helper.update();
}
-updateLight();

Note that at some level a PointLightHelper has no um, point. It just draws a small wireframe diamond. It could just as easily be any shape you want, just add a mesh to the light itself.

A PointLight has the added property of distance. If the distance is 0 then the PointLight shines to infinity. If the distance is greater than 0 then the light shines its full intensity at the light and fades to no influence at distance units away from the light.

Let's setup the GUI so we can adjust the distance.

const gui = new GUI();
gui.addColor(new ColorGUIHelper(light, 'color'), 'value').name('color');
gui.add(light, 'intensity', 0, 2, 0.01);
+gui.add(light, 'distance', 0, 40).onChange(updateLight);

makeXYZGUI(gui, light.position, 'position', updateLight);
-makeXYZGUI(gui, light.target.position, 'target', updateLight);

And now try it out.

Notice when distance is > 0 how the light fades out.

SpotLight

Spotlights are effectively a point light with a cone attached where the light only shines inside the cone. There's actually 2 cones. An outer cone and an inner cone. Between the inner cone and the outer cone the light fades from full intensity to zero.

To use a SpotLight we need a target just like the directional light. The light's cone will open toward the target.

Modifying our DirectionalLight with helper from above

const color = 0xFFFFFF;
const intensity = 1;
-const light = new THREE.DirectionalLight(color, intensity);
+const light = new THREE.SpotLight(color, intensity);
scene.add(light);
scene.add(light.target);

-const helper = new THREE.DirectionalLightHelper(light);
+const helper = new THREE.SpotLightHelper(light);
scene.add(helper);

The spotlight's cone's angle is set with the angle property in radians. We'll use our DegRadHelper from the texture article to present a UI in degrees.

gui.add(new DegRadHelper(light, 'angle'), 'value', 0, 90).name('angle').onChange(updateLight);

The inner cone is defined by setting the penumbra property as a percentage from the outer cone. In other words when penumbra is 0 then the inner code is the same size (0 = no difference) from the outer cone. When the penumbra is 1 then the light fades starting in the center of the cone to the outer cone. When penumbra is .5 then the light fades starting from 50% between the center of the outer cone.

gui.add(light, 'penumbra', 0, 1, 0.01);

Notice with the default penumbra of 0 the spotlight has a very sharp edge whereas as you adjust the penumbra toward 1 the edge blurs.

It might be hard to see the cone of the spotlight. The reason is it's below the ground. Shorten the distance to around 5 and you'll see the open end of the cone.

RectAreaLight

There's one more type of light, the RectAreaLight, which represents exactly what it sounds like, a rectangular area of light like a long fluorescent light or maybe a frosted sky light in a ceiling.

The RectAreaLight only works with the MeshStandardMaterial and the MeshPhysicalMaterial so let's change all our materials to MeshStandardMaterial

  ...

  const planeGeo = new THREE.PlaneBufferGeometry(planeSize, planeSize);
-  const planeMat = new THREE.MeshPhongMaterial({
+  const planeMat = new THREE.MeshStandardMaterial({
    map: texture,
    side: THREE.DoubleSide,
  });
  const mesh = new THREE.Mesh(planeGeo, planeMat);
  mesh.rotation.x = Math.PI * -.5;
  scene.add(mesh);
}
{
  const cubeSize = 4;
  const cubeGeo = new THREE.BoxBufferGeometry(cubeSize, cubeSize, cubeSize);
- const cubeMat = new THREE.MeshPhongMaterial({color: '#8AC'});
+ const cubeMat = new THREE.MeshStandardMaterial({color: '#8AC'});
  const mesh = new THREE.Mesh(cubeGeo, cubeMat);
  mesh.position.set(cubeSize + 1, cubeSize / 2, 0);
  scene.add(mesh);
}
{
  const sphereRadius = 3;
  const sphereWidthDivisions = 32;
  const sphereHeightDivisions = 16;
  const sphereGeo = new THREE.SphereBufferGeometry(sphereRadius, sphereWidthDivisions, sphereHeightDivisions);
-  const sphereMat = new THREE.MeshPhongMaterial({color: '#CA8'});
+ const sphereMat = new THREE.MeshStandardMaterial({color: '#CA8'});
  const mesh = new THREE.Mesh(sphereGeo, sphereMat);
  mesh.position.set(-sphereRadius - 1, sphereRadius + 2, 0);
  scene.add(mesh);
}

To use the RectAreaLight we need to include some extra three.js optional data

import * as THREE from './resources/three/r110/build/three.module.js';
+import {RectAreaLightUniformsLib} from './resources/threejs/r110/examples/jsm/lights/RectAreaLightUniformsLib.js';

and we need to call RectAreaLightUniformsLib.init

function main() {
  const canvas = document.querySelector('#c');
  const renderer = new THREE.WebGLRenderer({canvas});
+  RectAreaLightUniformsLib.init();

If you forget the data the light will still work but it will look funny so be sure to remember to include the extra data.

Now we can create the light

const color = 0xFFFFFF;
*const intensity = 5;
+const width = 12;
+const height = 4;
*const light = new THREE.RectAreaLight(color, intensity, width, height);
light.position.set(0, 10, 0);
+light.rotation.x = THREE.Math.degToRad(-90);
scene.add(light);

*const helper = new THREE.RectAreaLightHelper(light);
*light.add(helper);

One thing to notice is that unlike the DirectionalLight and the SpotLight, the RectAreaLight does not use a target. It just uses its rotation. Another thing to notice is the helper needs to be a child of the light. It is not a child of the scene like other helpers.

Let's also adjust the GUI. We'll make it so we can rotate the light and adjust its width and height

const gui = new GUI();
gui.addColor(new ColorGUIHelper(light, 'color'), 'value').name('color');
gui.add(light, 'intensity', 0, 10, 0.01);
gui.add(light, 'width', 0, 20).onChange(updateLight);
gui.add(light, 'height', 0, 20).onChange(updateLight);
gui.add(new DegRadHelper(light.rotation, 'x'), 'value', -180, 180).name('x rotation').onChange(updateLight);
gui.add(new DegRadHelper(light.rotation, 'y'), 'value', -180, 180).name('y rotation').onChange(updateLight);
gui.add(new DegRadHelper(light.rotation, 'z'), 'value', -180, 180).name('z rotation').onChange(updateLight);

makeXYZGUI(gui, light.position, 'position', updateLight);

And here is that.

One thing we didn't cover is that there is a setting on the WebGLRenderer called physicallyCorrectLights. It effects how light falls off as distance from light. It only affects PointLight and SpotLight. RectAreaLight does this automatically.

For lights though the basic idea is you don't set a distance for them to fade out, and you don't set intensity. Instead you set the power of the light in lumens and then three.js will use physics calculations like real lights. The units of three.js in this case are meters and a 60w light bulb would have around 800 lumens. There's also a decay property. It should be set to 2 for realistic decay.

Let's test that.

First we'll turn on physically correct lights

const renderer = new THREE.WebGLRenderer({canvas});
+renderer.physicallyCorrectLights = true;

Then we'll set the power to 800 lumens, the decay to 2, and the distance to Infinity.

const color = 0xFFFFFF;
const intensity = 1;
const light = new THREE.PointLight(color, intensity);
light.power = 800;
light.decay = 2;
light.distance = Infinity;

and we'll add gui so we can change the power and decay

const gui = new GUI();
gui.addColor(new ColorGUIHelper(light, 'color'), 'value').name('color');
gui.add(light, 'decay', 0, 4, 0.01);
gui.add(light, 'power', 0, 2000);

It's important to note each light you add to the scene slows down how fast three.js renders the scene so you should always try to use as few as possible to achieve your goals.

Next up let's go over dealing with cameras.

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