Achieving Transparent Backgrounds With Emissive Materials In Blender

Emissive materials in Blender are shader materials that emit light. They can be used to create transparency effects by making other materials partially see-through, allowing the emission to show through from underneath.

The emission strength can be controlled using shader nodes. By mixing an emissive shader with a transparent shader, you can see the emission glow through the transparency.

What are Emissive Materials and How Do They Create Transparency?

An emissive material shader in Blender emits light energy as photons from the material’s surface, illuminating the scene without needing external scene lights. The pixels for emissive materials are always rendered at 100% brightness, overriding shading and shadowing.

By making other materials in the scene partially transparent, the bright emissive material shining from underneath can be seen glowing through those surfaces. This creates a transparency effect where the emissive areas appear to shine out from within opaque objects.

For example, the inside of a glass lightbulb would use an emissive material, while the glass surface would use a transparent shader mixed with a glass shader. This way, the bright emissive material shines out through the transparent glass surface.

Advantages of Emissive Transparency

• Creates glowing see-through effects
• Provides additional scene illumination
• Allows selective transparency which hides other surface details
• Can simulate light emission from real-world emissive surfaces

Disadvantages of Emissive Transparency

• Can be computationally intensive in complex scenes
• Light details may be lost from the emissive material inside
• Can require adjusting transparency levels carefully
• Emission may overwhelm other shader details

Setting Up an Emissive Material in Blender

Here is the process for setting up a basic emissive material in Blender and applying it to an object:

1. Add a new material shader to Blender and rename it to something descriptive like “EmissiveSurface”.
2. In the Node Editor, add an Emission shader node and connect it to the Surface input of the Material Output node.
3. Turn up the Strength value on the Emission node to around 2-5 to increase the emission brightness.
4. Select the object you want to apply emission to, like a plane or cube.
5. In the Material Properties, assign the emissive material to that object by selecting it from the dropdown.

Now you have a basic emissive surface applied to create glowing illumination. From here you can adjust colors, strengths, make transparency mixes, and more.

Important Emission Settings

• Strength: Controls emission brightness levels.
• Color: Tints the emitted light color.
• Surface: Input for emission shader to feed color to surface.

Controlling the Strength of Emission

The Strength value on the Emission shader node determines the intensity of the emitted light. Higher values make the surface brighter.

Setting Emission Strength

There are a few ways to adjust and control emission strength values:

• Directly type a number like 2.5 into the Strength input field.
• Use a ColorRamp node to map brightness ranges to values.
• Connect a Math node like Multiply to dynamically adjust it.
• Drive strength with an animation curve for pulsating effects.
• Plug in a texture sample node to vary strength across the surface.

Typical Emission Strength Values

• 0.0 to 0.1 – Very low, almost no emission.
• 0.5 to 1 – Glowing embers or LED types.
• 2 to 5 – Bright holograms, neon, bulbs.
• 10+ – Very high, blazing fire, supernova.

The optimal value range depends greatly on your specific scene and desired effect. Going above 10 starts to give an extremely blown-out look unless that is what you require.

Making Other Materials Transparent to Show Emission

To allow an emissive material’s glow to shine through, other surface shaders need to be made transparent in some way. Here are some methods to accomplish this in Blender:

Add a Transparent Shader Mix

The easiest way is to mix your surface shader with a Transparent shader using an Add Shader or Mix Shader node. Plug the transparent shader into the surface input as well, then control the mix Factor value between 0.0 and 1.0 to set the see-through level.

Adjust Material Alpha and Ray Visibility

Lowering the Alpha value and Ray Visibility settings on a material will also introduce transparency for rays of light to pass through. This affects the overall material channel rather than mixing shaders.

Use a Holdout Shader

A Holdout shader can also simulate transparency by making light pass straight through without interacting with the surface, similar to alpha masking. This works well for creating uneven shaped emissive glows.

Sample Node Setup for Emissive Material with Transparency

Here is one example node workflow to mix an emission shader with a transparent shader in Blender:

1. Create the base emissive material with an Emission node feeding into the Surface socket.
2. Adjust the emissive color and strength values as needed.
3. Add a Transparent BSDF shader node.
4. Plug the Transparent BSDF into an Add Shader node, add the Emission shader into the other socket.
5. Use a Mix RGB node to mix between the Add Shader and Surface socket using a Factor input.
6. Change the Mix Factor to control transparency level and blend between full emissive and full transparent.

With this node setup, you have a way to easily mix and adjust the transparency level and emission brightness dynamically in the material.

Alternative Setup Methods

Some other ways to mix emissive and transparency shaders include:

• Using a Mix Shader node instead of Add Shader.
• Mixing the Transparent BSDF directly with the Surface socket.
• Feeding multiple shaders into a Fresnel and Layer Weight node setup.

The needs of your specific material will determine the best approach.

Rendering Considerations with Emissive Transparency

When working with rendering emissive transparency effects, there are some settings and technical considerations to keep in mind:

Sampling and Noise

Using branched path tracing is important for accurately sampling the emissive rays shining through transparent surfaces. Ensure branched path tracing is enabled in your render settings.

You may also need to increase the sample count to reduce noise from the emission ray effects. Adding more samples will give a cleaner render at the cost of longer render times.

Mesh Density and Light Leaks

Very low poly meshes can sometimes allow emission to “leak” through cracks between faces and edges. Adding supporting edge loops and increasing mesh density can improve this.

The Emission shader also works best on solid faces rather than wireframes, so meshes should be manifold without holes to get evenly distributed illumination.

Cycles vs. Eevee Renderer Differences

Cycles handles emissive transparency more accurately than Eevee, giving a closer match to final render results. For previewing, the EEVEE render workflow may require more test renders in Cycles to fine tune transparency mixing.

In Eevee, transparency and alpha mapping can also sometimes conflict with emission effects in complex shader node trees.

Common Questions and Issues

Here are some frequently asked questions that come up when working with emissive transparency in Blender:

How do I make the emissive glow pulsing or animated over time?

Use a Math or ColorRamp node to modulate the emission strength value over time with the Value node. You can also animate colors shifting using color mix nodes. Adding a bit of noise helps create organic flickering.

What if I want irregular random transparent shapes over the emission?

Using procedural noise textures mixed with the transparency factor input works well to create a more random abstract transparency pattern over the emission material.

Is there any faster preview method than full Cycles renders?

For quicker previewing, use Eevee and enable Bloom. This approximates the glow result. Just know that EEVEE simplification can hide potential noise issues compared to final Cycles.

Can I limit emission to only part of the surface?

Yes, using a Texture Coordinate node with a Wave Texture for influence masks lets you isolate emission to specific mesh regions. The Mix RGB node is useful for blending this type of effect.