Lately I’ve come to realize that the light on a painting as you’re working on it is as important as the light on whatever you are painting.
I’ve recently added a light over my easel that provides more illumination than anyone would actually shine on a painting that was being displayed. I tend to keep it off much of the time while painting, but turn it on periodically to check my work. Under a higher level of illumination, I often catch problems, especially in the deeper shadows. Without enough light, it’s easy to miss inaccuracies in value, hue, chroma, or gradation. These problems might not show up too strongly when the painting is displayed, but can be significant enough to cause noticeable errors.
Of course, the color of the light shining on your painting should be neutral enough that it does not itself introduce distortions and thereby lead you misunderstand hue relationships while mixing paint.