Nice explanation Terry,
I agree in the concept of "Light becoming Brighter" as in A topic becomes clearer, as you discover complementary facts, and have time to Meditate on the Body of Clues. This type of Gradual Understanding can take Drastic shifts also.. At times you can Discover information, that completely transforms the paradigm, and when this happens the Light moves to a completely different Path.
The Watchtower completely abuses this concept. The Watchtower's Light Got Bright at one time,when Russell was actually seeking Truth, however ever since they have been Turning the Light on and Off at will, simply to Support their Greed & Blasphemous Ways.As you mentioned, the Light cannot become bright, and then Become Dark, move to another Belief, and Return to the same Belief without any Forward Progress.
In the words of another Wise Man... "Let's Review, It's a Cult!"