I've been having a conversation with someone over on DA over torpedoes and phasers from TOS, and how the rest of Trek got the concept of phasers and torpedoes all wrong.
He states that in TOS, the torpedoes were not physical in anyway, instead being pure energy, and therefore the ship had unlimited photon torpedoes. This would explain why photon torpedoes, when fired, had a flare to them.
Sorry that I get involved here so late. The problem is quite simple, that at that time you did not have such a big budget for the visual effects. For that reason, the effects for phasers and torpedoes were initially the same. The "proximity blast" from "Balance of Terror" is exactly the same effect that was later used for the photon torpedoes. Leaving aside the dialogues, the "phasers" from that episode were simply torpedoes, just misnamed. This is also supported by the fact that later a separate phaser beam effect was introduced and the "proximity blast", beside the episode "Errand of Mercy", never used again.
