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# emissionDurationVariation

The range, in seconds, of randomized emission duration values. Animatable.

```
var emissionDurationVariation: CGFloat { get set }
```

## Discussion

Setting a nonzero value for this property randomizes the effect of the [`emissionDuration`](/documentation/SceneKit/SCNParticleSystem/emissionDuration) property. For each emission period, SceneKit randomly adjusts the duration by up to half the [`emissionDurationVariation`](/documentation/SceneKit/SCNParticleSystem/emissionDurationVariation) value. For example, if the [`emissionDuration`](/documentation/SceneKit/SCNParticleSystem/emissionDuration) value is `1.0` seconds and the [`emissionDurationVariation`](/documentation/SceneKit/SCNParticleSystem/emissionDurationVariation) value is `0.5` seconds, the system emits particles over a period of `0.75` to `1.25` seconds before stopping.

The default value is `0.0` seconds, specifying no randomization.

You can animate changes to this property’s value. See [Animating SceneKit Content](/documentation/SceneKit/animating-scenekit-content).

---

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