# Three.js Lighting

## Quick Start

```javascript
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.

```javascript
// 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.

```javascript
// 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).

```javascript
// 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

```javascript
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; // Blur radius (PCFSoftShadowMap only)

// 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.

```javascript
// 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

```javascript
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.

```javascript
// 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

```javascript
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.

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

// Must initialize uniforms first
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 RectAreaL

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