How do you use global illumination in Blender to create different moods and atmospheres?

Global Illumination (GI) in Blender is grounded in the concept that light sources aren't the sole emitters of light within a scene. Any surface that receives light also reflects a portion of it to other surfaces, thus generating indirect illumination. This process lends a sense of naturalness and coherence to the scene, affecting the colors and brightness of objects as they interact with their environment. GI introduces soft shadows, ambient occlusion, and caustics, which are intricate light patterns created when light interacts with transparent or reflective materials.

Global Illumination is what sets apart modern game visuals from the early 3D game era in the 90s. Without GI, a 3D scene will appear immediately dated, reminiscent of Nintendo 64 or Playstation games. With Blender, you can easily achieve global illumination in your scenes. Colors, light, and shadows look more natural, not artificial.

Blender offers two rendering engines that support Global Illumination (GI): Cycles and Eevee. Cycles is a ray-tracing engine renowned for its precision and intricate results, as it meticulously calculates the paths of light rays in the scene. Eevee, on the other hand, is a real-time engine that prioritizes speed and interactivity, utilizing approximations and shortcuts, albeit with certain limitations. To enable GI in Blender, you must choose between Cycles and Eevee as your render engine within the Render Properties panel. Following this selection, you'll need to fine-tune the settings for the World and Render layers, depending on your chosen engine.

Cycles makes achieving GI very easy. It's basically on by default. Adding an HDRI makes it more obvious., GI in Eevee is trickier - as it requires adding an Irradiance Volume to the scene first. Then, you must press the "Bake Indirect Lighting" button in the Render Properties of Blender. Eevee will then bake indirect light, which helps bring the scene's appearance closer to what Cycles would achieve with its GI.

GI is enabled in Cycles by default. It doesn't require any extra work on the designer's part. However, you can enhance the GI by adding a high-quality HDRI as an Environment Texture in the Shader Editor (set to World Mode).

In Blender's Cycles engine, Global Illumination (GI) is active by default, as it traces the paths of light rays that scatter and bounce within the scene. However, you have the flexibility to fine-tune the quality and intensity of GI by adjusting parameters within the Render Properties panel. The "Samples" parameter controls the number of light rays traced for each pixel in the render, while "Bounces" determines how many times a light ray can bounce before ceasing. Additionally, "Clamp" sets the maximum brightness of a light ray, which can help reduce unwanted artifacts (fireflies) but may darken the scene and compromise details.

In ccyles , I am very disappointed with the GI, always the scene, particuarly outdoors has really dark shadows. No such problem in either vray or Arnold You can fake it by using Fast GI approximation but it looks a bit wrong

GI in Eevee requires some extra steps, as it doesn't use GI by default. Add an Irradiance Volume to your scene using the Shift + A keys (under the Light Probe category). Then resize and position it so that it engulfs your whole scene, or at least the section of your scene that you want GI in. Then, in the Render Properties of Blender (on the right-side of the window), look for the "Indirect Lighting" subpanel, and press the "Bake Indirect Lighting" button there. Eevee will then calculate and bake indirect lighting based on the Irradiance Volume. Note that the Irradiance Volume has two boxes - the outer box determines where its effect completely fades out. Anything inside the inner box receives 100% of the Irradiance Volume's effect.

Carefully positioned lights can create a really compelling atmosphere with GI. Similarly, emissive materials can also add to the effect of GI on the scene's atmosphere. Add emissive materials in key areas of your scene to bring attention to them. After baking indirect lighting in Eevee, emissive materials will create additional light bounces that can dramatically add to the mood of the scene.