"Mostly I'm not sure how there is light in the scene with no Ambient being used?"

The Ambient channel isn't special. The name implies that it is, but it isn't. It simply draws whatever you plug in, without taking into account any light sources. 

That is the definition of "glow" - to give off a specific, non-zero amount of light regardless of how little, if any, is arriving.

The Alternate_Diffuse channel does exactly the same thing. I could just as easily have used the Ambient. The reason I didn't is because I have a function in matmatic that routinely just uses Alternate_Diffuse. By doing so, I perform less typing. (I only have to set it - don't need to set the Ambient_Value to 1 as well.)

Look at it this way: If the water heater is turned off, then the hot water tap yields cold water. 

Yes I used the hot water tap (Alternate_Diffuse) to get cold water (glow) because I turned off the water heater (did not use a Diffuse-type of node).

If I plug a Diffuse node into Ambient, then it isn't ambient anymore - it's diffuse reflection.

If I plug a Specular node into Alternate_Diffuse, then it isn't diffuse or ambient - it's specular.

The channels that do what they're told to do are capable to doing whatever you tell them to do. 

These are: Alternate_Diffuse, Alternate_Specular, Reflection_Color, Refraction_Color, Ambient, and Translucence_Color.

There are some subtle differences between them, but for the beginner's understanding, they are interchangeable.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)