threejs-lighting – Other skill for AI agents

Three.js Lighting

When to Use

• You need to add or tune lighting in a Three.js scene.
• The task involves light types, shadows, environment lighting, or lighting performance tradeoffs.
• You want to improve scene readability, realism, or mood through Three.js lighting setup.

Quick Start

import * as THREE from "three";

// Basic lighting setup
const ambientLight = new THREE.AmbientLight(0xffffff, 0.5);
scene.add(ambientLight);

const directionalLight = new THREE.DirectionalLight(0xffffff, 1);
directionalLight.position.set(5, 5, 5);
scene.add(directionalLight);

Light Types Overview

| Light | Description | Shadow Support | Cost |

| ---------------- | ---------------------- | -------------- | -------- |

| AmbientLight | Uniform everywhere | No | Very Low |

| HemisphereLight | Sky/ground gradient | No | Very Low |

| DirectionalLight | Parallel rays (sun) | Yes | Low |

| PointLight | Omnidirectional (bulb) | Yes | Medium |

| SpotLight | Cone-shaped | Yes | Medium |

| RectAreaLight | Area light (window) | No\* | High |

\*RectAreaLight shadows require custom solutions

AmbientLight

Illuminates all objects equally. No direction, no shadows.

// AmbientLight(color, intensity)
const ambient = new THREE.AmbientLight(0xffffff, 0.5);
scene.add(ambient);

// Modify at runtime
ambient.color.set(0xffffcc);
ambient.intensity = 0.3;

HemisphereLight

Gradient from sky to ground color. Good for outdoor scenes.

// HemisphereLight(skyColor, groundColor, intensity)
const hemi = new THREE.HemisphereLight(0x87ceeb, 0x8b4513, 0.6);
hemi.position.set(0, 50, 0);
scene.add(hemi);

// Properties
hemi.color; // Sky color
hemi.groundColor; // Ground color
hemi.intensity;

DirectionalLight

Parallel light rays. Simulates distant light source (sun).

// DirectionalLight(color, intensity)
const dirLight = new THREE.DirectionalLight(0xffffff, 1);
dirLight.position.set(5, 10, 5);

// Light points at target (default: 0, 0, 0)
dirLight.target.position.set(0, 0, 0);
scene.add(dirLight.target);

scene.add(dirLight);

DirectionalLight Shadows

dirLight.castShadow = true;

// Shadow map size (higher = sharper, more expensive)
dirLight.shadow.mapSize.width = 2048;
dirLight.shadow.mapSize.height = 2048;

// Shadow camera (orthographic)
dirLight.shadow.camera.near = 0.5;
dirLight.shadow.camera.far = 50;
dirLight.shadow.camera.left = -10;
dirLight.shadow.camera.right = 10;
dirLight.shadow.camera.top = 10;
dirLight.shadow.camera.bottom = -10;

// Shadow softness
dirLight.shadow.radius = 4; // Filtering behavior depends on renderer/version/shadow type; verify the installed reference

// Shadow bias (fixes shadow acne)
dirLight.shadow.bias = -0.0001;
dirLight.shadow.normalBias = 0.02;

// Helper to visualize shadow camera
const helper = new THREE.CameraHelper(dirLight.shadow.camera);
scene.add(helper);

PointLight

Emits light in all directions from a point. Like a light bulb.

// PointLight(color, intensity, distance, decay)
const pointLight = new THREE.PointLight(0xffffff, 1, 100, 2);
pointLight.position.set(0, 5, 0);
scene.add(pointLight);

// Properties
pointLight.distance; // Maximum range (0 = infinite)
pointLight.decay; // Light falloff (physically correct = 2)

PointLight Shadows

pointLight.castShadow = true;
pointLight.shadow.mapSize.width = 1024;
pointLight.shadow.mapSize.height = 1024;

// Shadow camera (perspective - 6 directions for cube map)
pointLight.shadow.camera.near = 0.5;
pointLight.shadow.camera.far = 50;

pointLight.shadow.bias = -0.005;

SpotLight

Cone-shaped light. Like a flashlight or stage light.

// SpotLight(color, intensity, distance, angle, penumbra, decay)
const spotLight = new THREE.SpotLight(0xffffff, 1, 100, Math.PI / 6, 0.5, 2);
spotLight.position.set(0, 10, 0);

// Target (light points at this)
spotLight.target.position.set(0, 0, 0);
scene.add(spotLight.target);

scene.add(spotLight);

// Properties
spotLight.angle; // Cone angle (radians, max Math.PI/2)
spotLight.penumbra; // Soft edge (0-1)
spotLight.distance; // Range
spotLight.decay; // Falloff

SpotLight Shadows

spotLight.castShadow = true;
spotLight.shadow.mapSize.width = 1024;
spotLight.shadow.mapSize.height = 1024;

// Shadow camera (perspective)
spotLight.shadow.camera.near = 0.5;
spotLight.shadow.camera.far = 50;
spotLight.shadow.camera.fov = 30;

spotLight.shadow.bias = -0.0001;

// Focus (affects shadow projection)
spotLight.shadow.focus = 1;

RectAreaLight

Rectangular area light. Great for soft, realistic lighting.

import { RectAreaLightHelper } from "three/examples/jsm/helpers/RectAreaLightHelper.js";
import { RectAreaLightUniformsLib } from "three/examples/jsm/lights/RectAreaLightUniformsLib.js";

// Must initialize uniforms first (WebGL renderer only)
RectAreaLightUniformsLib.init();

// RectAreaLight(color, intensity, width, height)
const rectLight = new THREE.RectAreaLight(0xffffff, 5, 4, 2);
rectLight.position.set(0, 5, 0);
rectLight.lookAt(0, 0, 0);
scene.add(rectLight);

// Helper
const helper = new RectAreaLightHelper(rectLight);
rectLight.add(helper);

// Works with MeshStandardMaterial, MeshPhysicalMaterial
// r183: Clearcoat on MeshPhysicalMaterial is now properly lit by RectAreaLight
// Does not cast shadows natively

Shadow Setup

Enable Shadows

// 1. Enable on renderer
renderer.shadowMap.enabled = true;
renderer.shadowMap.type = THREE.PCFSoftShadowMap;

// Shadow map types:
// THREE.BasicShadowMap - fastest, low quality
// THREE.PCFShadowMap - default, filtered
// THREE.PCFSoftShadowMap - softer edges
// THREE.VSMShadowMap - variance shadow map

// 2. Enable on light
light.castShadow = true;

// 3. Enable on objects
mesh.castShadow = true;
mesh.receiveShadow = true;

// Ground plane
floor.receiveShadow = true;
floor.castShadow = false; // Usually false for floors

Optimizing Shadows

// Tight shadow camera frustum
const d = 10;
dirLight.shadow.camera.left = -d;
dirLight.shadow.camera.right = d;
dirLight.shadow.camera.top = d;
dirLight.shadow.camera.bottom = -d;
dirLight.shadow.camera.near = 0.5;
dirLight.shadow.camera.far = 30;

// Fix shadow acne
dirLight.shadow.bias = -0.0001; // Depth bias
dirLight.shadow.normalBias = 0.02; // Bias along normal

// Shadow map size (balance quality vs performance)
// 512 - low quality
// 1024 - medium quality
// 2048 - high quality
// 4096 - very high quality (expensive)

Contact Shadows

Do not import three/examples/jsm/objects/ContactShadows.js: this guide does not identify a verified Three.js addon at that path. In a React Three Fiber project, [Drei's ContactShadows](https://drei.docs.pmnd.rs/staging/contact-shadows) is a separate component/dependency; inspect its version and performance cost before adoption. Plain Three.js projects need a reviewed render-target implementation or a supported alternative.

Light Helpers

import { RectAreaLightHelper } from "three/examples/jsm/helpers/RectAreaLightHelper.js";

// DirectionalLight helper
const dirHelper = new THREE.DirectionalLightHelper(dirLight, 5);
scene.add(dirHelper);

// PointLight helper
const pointHelper = new THREE.PointLightHelper(pointLight, 1);
scene.add(pointHelper);

// SpotLight helper
const spotHelper = new THREE.SpotLightHelper(spotLight);
scene.add(spotHelper);

// Hemisphere helper
const hemiHelper = new THREE.HemisphereLightHelper(hemi, 5);
scene.add(hemiHelper);

// RectAreaLight helper
const rectHelper = new RectAreaLightHelper(rectLight);
rectLight.add(rectHelper);

// Update helpers when light changes
dirHelper.update();
spotHelper.update();

Environment Lighting (IBL)

Image-Based Lighting using HDR environment maps.

import { RGBELoader } from "three/examples/jsm/loaders/RGBELoader.js";

const rgbeLoader = new RGBELoader();
rgbeLoader.load("environment.hdr", (texture) => {
  texture.mapping = THREE.EquirectangularReflectionMapping;

  // Set as scene environment (affects all PBR materials)
  scene.environment = texture;

  // Optional: also use as background
  scene.background = texture;
  scene.backgroundBlurriness = 0; // 0-1, blur the background
  scene.backgroundIntensity = 1;
});

// PMREMGenerator for better reflections
const pmremGenerator = new THREE.PMREMGenerator(renderer);
pmremGenerator.compileEquirectangularShader();

rgbeLoader.load("environment.hdr", (texture) => {
  const envMap = pmremGenerator.fromEquirectangular(texture).texture;
  scene.environment = envMap;
  texture.dispose();
  pmremGenerator.dispose();
});

Cube Texture Environment

const cubeLoader = new THREE.CubeTextureLoader();
const envMap = cubeLoader.load([
  "px.jpg",
  "nx.jpg",
  "

… (full content is in the download package)