Emissive Materials in Unity

 Emissive materials in Unity. Verbatim extracts from https://learn.unity.com/tutorial/introduction-to-lighting-and-rendering#5c7f8528edbc2a002053b532

Emissive Materials

Whilst Area Lights are not supported by Precomputed Realtime GI, similar soft lighting effects are still possible using ‘Emissive Materials.’ Like Area Lights, emissive materials emit light across their surface area. They contribute to bounced light in your scene and associated properties such as color and intensity can be changed during gameplay.

‘Emission’ is a property of the Standard Shader which allows static objects in our scene to emit light. By default the value of ‘Emission’ is set to zero. This means no light will be emitted by objects assigned materials using the Standard Shader. The HDR color picker can be used to select colors with intensities beyond the 0-1 range in order to create bright light effects similar to those of Area Lights.

There is no range value for emissive materials but light emitted will again falloff at a quadratic rate. Emission will only be received by objects marked as ‘Static’ or “Lightmap Static’ from the Inspector. Similarly, emissive materials applied to non-static, or dynamic geometry such as characters will not contribute to scene lighting.

However, materials with an emission above zero will still appear to glow brightly on-screen even if they are not contributing to scene lighting. This effect can also be produced by selecting ‘None’ from the Standard Shader’s ‘Global Illumination’ Inspector property. Self-illuminating materials like these are a useful way to create effects such as neons or other visible light sources.

Simple neon sign created using the ‘Emission’ property of Unity’s Standard Shader. Notice how the emission from the sign is still shadowed by static geometry - in this case, the sphere.

Emissive materials only directly affect static geometry in your scene. If you need dynamic, or non-static geometry - such as characters, to pick up light from emissive materials, Light Probes must be used. Changing emission values at gameplay will update Light Probes interactively and the results will be visible on any objects presently receiving light from those probes