Anyone remember when the refit Enterprise was launched in "Star Trek: The Motion Picture"? It is implied that the "glow" of the main deflector dish is actually a product of the matter/antimatter reactor in the secondary hull coming online. In the movie, IIRC the moment the intermix starts up it cuts to an exterior view of the Enterprise and the "deflector dish" starts to glow. A glow which grows steadily. Of course in this regard it helps to remember as evidenced by the original "cutaway" poster of the refit Enterprise, the matter/antimatter intermix chamber was NOT a simple vertical cylinder but the entire front end of the engineering hull.