Glow is essentially a factor of value rather than color. How is this achieved? Paint a black canvas and let it dry. On your finger place a little white and with small circular smudging motion apply it somewhere to the canvas. It should now look like a milky smudge. Next take a pinpoint of paint on the end of your finger and touch it once in the middle of the smudge. The result is the essence of glow, total value differential as well as the milky area being a transmission area that will discomfort the eye sufficiently to avoid looking to the point of the light. That is the why we don't want to look directly at the sun. It is discomforting. For great glow or luminosity you must set out to discomfort the eye, that is the secret. To do that the transition (the halo) is the key.

	Fig 1.Here are a series of milky smudges
	Fig 2. When we combine them we create our glow. Note how I have deliberately offset to white center in an effort to further disturb the eye.
	Fig 3. Now I add a little color (any will do) some dark shapes between the spectator and the light and a halo. The halo and spike here are artificial - like the ones made by a camera lens reflection - it is not the same type of halo in the example below.

What discomforts the eye in painting is similar to what discomforts the ear in music. Music is a 'transition' experience in which time is a fixed element (beat). But the eye roves the painted surface in a manner hopefully controlled by the painter. The painter may cleverly force a discomfort in much the same manner a jazz musician will use a discordant note to lay emphasis on a beautiful (intoxicating) chord. What discomforts the eye can be many things, adjacent compliments, illogical form, concave mirrors or, what I mentioned above, unfocused edges. (Rothko used fuzzy rectangles to try and induce a extra translucent brilliance to his plain color areas - it is an old formula).
Why a discomfort? Because the eye naturally avoids looking at bright objects so to paint one the discomfort must be artificially induced. Painting suns and moons was usually referred to as a 'brave exercise' and avoided by all but the most accomplished landscape artists (Turner was accomplished while VanGough experimented). We can never paint surfaces as light as natural light so we must use device and illusion to convince the eye what it is seeing is a light as it should be... that is the fun of illusion!

Painting glow without showing the light source.
Here the principles are the same with the darks superimposed over the lights.

Detail of morning glow from another painting I did for the 'Bounty' series.