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# areaRadius

The radius, in units of local coordinate space, of the area from which light emanates.

```
var areaRadius: Float { get set }
```

## Discussion

The effect of radius on a light’s shape depends on the value of its inherited [`lightType`](/documentation/ModelIO/MDLLight/lightType) property:

- [`MDLLightType.linear`](/documentation/ModelIO/MDLLightType/linear): The light is shaped like a line segment, centered on the origin of its local coordinate space and extending along the x-axis with a total length of twice the [`areaRadius`](/documentation/ModelIO/MDLAreaLight/areaRadius) value.
- [`MDLLightType.discArea`](/documentation/ModelIO/MDLLightType/discArea): The light is shaped like a circle or ellipse in the xy-plane of its local coordinate space. If the [`aspect`](/documentation/ModelIO/MDLAreaLight/aspect) value is `1.0`, the [`areaRadius`](/documentation/ModelIO/MDLAreaLight/areaRadius) value is the circle’s radius. If the [`aspect`](/documentation/ModelIO/MDLAreaLight/aspect) value is less than one, the [`areaRadius`](/documentation/ModelIO/MDLAreaLight/areaRadius) value is the major radius of the ellipse, and the minor radius is equal to the [`areaRadius`](/documentation/ModelIO/MDLAreaLight/areaRadius) value times the [`aspect`](/documentation/ModelIO/MDLAreaLight/aspect) value.
- [`MDLLightType.rectangularArea`](/documentation/ModelIO/MDLLightType/rectangularArea): The light is shaped like a rectangle in the xy-plane of its local coordinate space. If the [`aspect`](/documentation/ModelIO/MDLAreaLight/aspect) value is `1.0`, the light is a square and [`areaRadius`](/documentation/ModelIO/MDLAreaLight/areaRadius) value is half the square’s width or length. If the [`aspect`](/documentation/ModelIO/MDLAreaLight/aspect) value is less than one, the [`areaRadius`](/documentation/ModelIO/MDLAreaLight/areaRadius) value is half the rectangle’s longer dimension, and the shorter dimension is the [`areaRadius`](/documentation/ModelIO/MDLAreaLight/areaRadius) value, times the [`aspect`](/documentation/ModelIO/MDLAreaLight/aspect) value, times two.
- [`MDLLightType.superElliptical`](/documentation/ModelIO/MDLLightType/superElliptical): The light is shaped like a superellipse—a two-dimensional figure in the xy-plane of its local coordinate space that can vary between shapes such as stars, diamonds, circles, and squares with rounded corners. The [`superEllipticPower`](/documentation/ModelIO/MDLAreaLight/superEllipticPower) property determines the general shape of the light, and the [`aspect`](/documentation/ModelIO/MDLAreaLight/aspect) property controls the ratio of the longer and shorter dimensions of the shape.

---

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