Question: From WWDC2016 `Advance SceneKit Rendering` Guide I found that SCNLight have a new type of light -- **IESLight**. *But I found that it couldn't cast shadows*. 
[![enter image description here](https://i.stack.imgur.com/TCt7f.png)](https://i.stack.imgur.com/TCt7f.png)

left is IESLight, right is SpotLight.

Answer: 
It depends on the ies profile: if it describes a 360° falloff then it is consider as an Omni light and it won t cast shadow. If the angle is < 180° then It will be considered as a spot and it will cast shadow.
I think I dismiss one point! The doc say that 

> 
> Geometries illuminated by the light cast shadows **only if** the value of this property is YES and the type property of the light is **SCNLightTypeSpot or SCNLightTypeDirectional**. The default value is NO.
> 
> 
> 

So I think why IESLight could not cast shadows. Thanks for reading.