Not necessarily. If you are making a painting, you don't have the ability to make some sections literally brighter (higher luminescence) because you don't reall

Not necessarily. If you are making a painting, you don't have the ability to make some sections literally brighter (higher luminescence) because you don't really have control over the lighting conditions, and oil paints only give you so much ability to adjust reflectance. So what you do is subtly adjust things like tone, texture, detail or technique to 'trick' the human perceptual system into thinking the difference is there. These tricks are what imparts that life-like quality into the old master's works.