Textures for Visualization - 3D for Graphic Designers - page 167

The first thing you will need to do is essentially eliminate any light in the scene before moving on:
1. Start by hiding (or deleting) the Directional Light. You will then be able to more clearly see the
effect of the Ambient Intensity setting. Instead of a black scene, you will see a flat, dark gray.
2. In the Render viewport, select the Shader Tree tab, and select Render.
3. Click the Global Illumination tab and set Ambient Intensity to 0. The resulting render preview is a
black screen. Though this may seem like a step backward, it actually gives a clean slate to work from.