Version: 2022.1

Using Lights

# 光源类型

• Point Light, a Light that’s located at a point in the Scene and emits light in all directions equally
• Spot Light, a Light that’s located at a point in the Scene and emits light in a cone shape
• Directional Light, a Light that’s located infinitely far away and emits light in one direction only
• Area Light, a Light that’s defined by a rectangle or disc in the Scene, and emits light in all directions uniformly across its surface area but only from one side of the rectangle or disc

## Point Lights

A Point Light is located at a point in space and sends light out in all directions equally. The direction of light hitting a surface is the line from the point of contact back to the center of the light object. The intensity diminishes with distance from the light, reaching zero at a specified range. Light intensity is inversely proportional to the square of the distance from the source. This is known as ‘inverse square law’ and is similar to how light behaves in the real world.

## Spot Lights

Like a Point Light, a Spot Light has a specified location and range over which the light falls off. However, a Spot Light is constrained to an angle, resulting in a cone-shaped region of illumination. The center of the cone points in the forward (Z) direction of the light object. Light also diminishes at the edges of a Spot Light’s cone. Widening the angle increases the width of the cone and with it increases the size of this fade, known as the ‘penumbra’.

## Directional Lights

Directional Lights are useful for creating effects such as sunlight in your scenes. Behaving in many ways like the sun, directional lights can be thought of as distant light sources which exist infinitely far away. A Directional Light doesn’t have any identifiable source position and so the light object can be placed anywhere in the scene. All objects in the scene are illuminated as if the light is always from the same direction. The distance of the light from the target object isn’t defined and so the light doesn’t diminish.

By default, every new Unity scene contains a Directional Light. This is linked to the procedural sky system defined in the Environment Lighting section of the Lighting Panel (Lighting>Scene>Skybox). You can change this behaviour by deleting the default Directional Light and creating a new light or simply by specifying a different GameObject from the ‘Sun’ parameter (Lighting>Scene>Sun).

## Area Lights

You can define an Area Light by one of two shapes in space: a rectangle or a disc. An Area Light emits light from one side of that shape. The emitted light spreads uniformly in all directions across that shape’s surface area. The Range property determines the size of that shape. The intensity of the illumination provided by an Area Light diminishes at a rate determined by the inverse square of the distance from the light source (see inverse square law). Because this lighting calculation is quite processor-intensive, Area Lights aren’t available at runtime and can only be baked into lightmaps.

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Using Lights