NEW IN R21
In addition to the simple coloring of a volume, the Emission node can be used to assign self-illumination proprties. Think of an explosion cloud, for example, or a flame as a volume. These types of effects can also actively emit light. Often, these properties can, for example, be linked to the simulated temperature of a volume so that hot areas of a volume emit light. The emission gradient can, for example, be used to make the cooler areas luminous using the colors on the left end of the gradient. The luminous colors of the hotter areas are then created by the colors at the right end of the gradient. The intenstiy of the luminous effect can also be affected using the Emission Strength setting.
Details about using the color gradient can be found under Color Gradient in Nodes.