I am actually if the opinion that the dungeon in Twilight Princess is in fact the "Temple Of Light". Yes, THE Temple of Light. The very same one that is located in the Sacred Realm where the Triforce is said to reside. I speculate this because it has some evidence to it but, like all theories, has flaws.
Firstly, it is an extension of the existing Temple Of Time, the entrance where the chanty "ee ee, ee ee ee etc." music plays. Since OoT, the Temple Of Light's entrance was said to be the Temple Of Time, with the Masted Sword as the key to it.
This happens in Twilight Princess. And after Link strikes the sword in the pedestal of time, stairs (made of Light!) appear, leading to the dungeon/temple. I can prove this because when you die (or quit) you respawn at that place after the stairs made of light. So, the Temple If Time is merely the entrance.
Secondly, the dungeon is absolutely saturated with symbols of light. At the very top where you fight the darknut, there is a massive symbol of light on the floor.
However, here are flaws: if Zant or Ganondorf could get to the Temple Of Light, why didn't they just grab the Triforce. The other issue, how could they even get in there, they need the Master Sword. And no one can touch the Master Sword unless your as benevolent as Link. I don't think the Temple constructed by the godesses would just idly let evil guys from entering whenever they felt like it but Link needed to get the Master Sword.
Simple answer could be: No one cares. Ends justify the means. Makes sense?