When we are painting a scene or some characters but we do not mark the contrast of lights and shadows, that is, everything has a smooth tonal graduation and the little shadows are mixed with the objects themselves… then we are creating an atmosphere or diffused lighting deployed and a great source of scattered light. In the absence of a strong focus on linear light power decreases and contrasts the ways that are more integrated and smooth.
Example of diffuse light in a painting:
William Turner, Storm in the snow. The white light and the snow are invading the picture on the top and towards the down side where we see the characters.