Looking at a collection of landscape paintings, I found that the paintings that were most interesting to me had a compelling area that seemed to emanate light, to "glow". I remember reading somewhere that in a painting, an area of glow seems to expand beyond its painted boundaries.
To discover how to achieve this in class, we each examined a painting with an area that glowed. We deliberately worked to reproduce the glow that we saw in our example.
Here is what seems to work. To achieve an area that glows, make an area of pure clean light color. Transition from this color with a color in line on the color wheel (e.g.. light pale yellow, follow with a light, pale yellow orange, then light red orange or starting with white, follow with light, pale yellow). Follow this with a middle value of a chromatic neutral. A "chromatic neutral" reads as a color's name (e.g. instead of grey, a chromatic neutral is a greyed "purple").
Here is a subtle example of the effect of a chromatic neutral green compared to a more "clean" intense green beside the area that we want to "glow". The less intense green on the left grape makes the glow more effective than the brighter green on the grape on the right.
Mom, Wife, Former Pediatrician, One who LOVES color, creativity, paint, and lifelong learning.