To make light pass through glass in Blender EEVEE, you need to properly configure both your material shader and the EEVEE render settings.
A key technique, as suggested by references, involves using a Transparent BSDF node mixed with your glass shader.
Shader Node Setup for Transparent Glass
For light to effectively pass through your glass material, you typically need a shader setup that allows for transparency. While a standard Glass BSDF node exists, achieving realistic light transmission and transparency in EEVEE often requires additional steps or alternative approaches.
One effective method is to mix your primary glass shader (like a Principled BSDF with high Transmission or a Glass BSDF) with a Transparent BSDF.
- Add your main glass shader (e.g., Principled BSDF with High Transmission or Glass BSDF).
- Add a Transparent BSDF node.
- Add a Mix Shader node.
- Connect your main glass shader output to one of the shader inputs of the Mix Shader.
- Connect the Transparent BSDF output to the other shader input of the Mix Shader.
- Connect the output of the Mix Shader to the Material Output node's Surface input.
As highlighted in the provided reference: "And finally we also need a sample transparent bstf. And also connect it to the mix Shader node and as you can see now all the light goes to the glass. And of course we have set it way too high." This illustrates that mixing in the Transparent BSDF helps light pass through, but the Factor of the Mix Shader needs careful adjustment. A factor of 1 for the Transparent BSDF would make the object completely invisible, so you'll need to control the mix using a driver, fresnel, or other means to achieve the desired balance between reflection/refraction and transparency.
EEVEE Render Settings
Beyond the material shader, specific settings within the EEVEE render properties are crucial for light and transparency to work correctly.
Navigate to the Render Properties tab (the camera icon).
- Transmission: Enable Screen Space Reflections and expand the settings. Check the Transmission box. This allows light passing through transparent/translucent materials to interact correctly with objects behind them within the screen space.
- Refraction: Also within Screen Space Reflections, enable Refraction. This is essential for bending light as it passes through the glass. Adjusting the 'IOR' (Index of Refraction) in your material's shader controls the degree of this bending.
- Alpha Hashed/Blend: In the Material Properties tab, under Settings > Blend Mode, for complex transparency (like overlapping glass surfaces), you might need to change the default 'Opaque' to 'Alpha Hashed' or 'Alpha Blend'. 'Alpha Hashed' generally works well for multiple layers of transparency in EEVEE.
- Caustics: While EEVEE doesn't render realistic caustics like Cycles, enabling Shadows > Soft Shadows can sometimes give a slightly more diffuse light pattern through transparent objects.
By combining the appropriate shader setup, potentially involving a Transparent BSDF mixed with your main glass material, and configuring these crucial EEVEE render settings, you can effectively allow light to pass through your glass objects in Blender EEVEE.