# How to set Alpha tree Transmittance of light

**URL:** <https://forum.babylonjs.com/t/how-to-set-alpha-tree-transmittance-of-light/43296>\
**Category:** Questions\
**Tags:** lighting, material\
**Created:** [August 14, 2023, 9:54am UTC](https://forum.babylonjs.com/t/how-to-set-alpha-tree-transmittance-of-light/43296 "2023-08-14T09:54:09Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![zhangyahan](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/zhangyahan/32/31789_2.png) [@zhangyahan](https://forum.babylonjs.com/u/zhangyahan)\
**Post date:** [August 14, 2023, 9:54am UTC](https://forum.babylonjs.com/t/how-to-set-alpha-tree-transmittance-of-light/43296/1 "2023-08-14T09:54:09Z")

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How to make the back of the tree in this example look like light is passing through. Now the back side of the tree doesn’t get light at all, and that’s true because the back side doesn’t get light, is there any way to get light through the tree.  
This should be a little help: [How You Expose the Light by Capturing it? #OpenLightBook Chapter 7 • Creative Shrimp](https://www.creativeshrimp.com/translucent-grass-lighting-tutorial-book-07.html)

> **[Babylon.js Playground](https://playground.babylonjs.com/#ZSA6Z3)**
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**Author:** ![carolhmj](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/carolhmj/32/25918_2.png) [@carolhmj](https://forum.babylonjs.com/u/carolhmj)\
**Post date:** [August 14, 2023, 11:03am UTC](https://forum.babylonjs.com/t/how-to-set-alpha-tree-transmittance-of-light/43296/2 "2023-08-14T11:03:34Z")

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You could try playing with the subsurface parameters of the PBR material: [Mastering PBR Materials | Babylon.js Documentation (babylonjs.com)](https://doc.babylonjs.com/features/featuresDeepDive/materials/using/masterPBR#sub-surface)

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**Author:** ![zhangyahan](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/zhangyahan/32/31789_2.png) [@zhangyahan](https://forum.babylonjs.com/u/zhangyahan)\
**Post date:** [August 15, 2023, 2:47am UTC](https://forum.babylonjs.com/t/how-to-set-alpha-tree-transmittance-of-light/43296/3 "2023-08-15T02:47:08Z")

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Yes, this is what I want, but why is it that after I set subSurface in Blender and then load it in Babylon, there is no manifestation of subSurface?

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**Author:** ![carolhmj](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/carolhmj/32/25918_2.png) [@carolhmj](https://forum.babylonjs.com/u/carolhmj)\
**Post date:** [August 15, 2023, 1:38pm UTC](https://forum.babylonjs.com/t/how-to-set-alpha-tree-transmittance-of-light/43296/4 "2023-08-15T13:38:24Z")

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Are you using Blender’s default glTF exporter?

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**Author:** ![zhangyahan](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/zhangyahan/32/31789_2.png) [@zhangyahan](https://forum.babylonjs.com/u/zhangyahan)\
**Post date:** [August 16, 2023, 2:02am UTC](https://forum.babylonjs.com/t/how-to-set-alpha-tree-transmittance-of-light/43296/5 "2023-08-16T02:02:58Z")

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Yes, I’m use belnder default glTF exporter.

 ![image](https://us1.discourse-cdn.com/flex024/uploads/babylonjs/original/3X/f/6/f62ce046c167df2213c7a976345ff8e96079369a.jpeg)

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**Author:** ![sebavan](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/sebavan/32/57_2.png) [@sebavan](https://forum.babylonjs.com/u/sebavan)\
**Post date:** [August 18, 2023, 3:20pm UTC](https://forum.babylonjs.com/t/how-to-set-alpha-tree-transmittance-of-light/43296/6 "2023-08-18T15:20:05Z")

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This would require the subsurface extension of GLTF which is not available yet so it is probably why Blender does not export it.

cc @bghgary to confirm.

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**Author:** ![bghgary](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/bghgary/32/48532_2.png) [@bghgary](https://forum.babylonjs.com/u/bghgary)\
**Post date:** [August 18, 2023, 3:54pm UTC](https://forum.babylonjs.com/t/how-to-set-alpha-tree-transmittance-of-light/43296/7 "2023-08-18T15:54:31Z")

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As @sebavan says, surface scattering extension is not yet available other than in a proposed state. Here is the PR for it: [KHR\_materials\_subsurface by bsdorra · Pull Request #1928 · KhronosGroup/glTF (github.com)](https://github.com/KhronosGroup/glTF/pull/1928)

There is also another proposed extension for diffuse transmission that might work for this case: [KHR\_materials\_diffuse\_transmission by proog128 · Pull Request #1825 · KhronosGroup/glTF (github.com)](https://github.com/KhronosGroup/glTF/pull/1825)

Unfortunately, both of these are not ready to use yet.