Came across this discussion again last night.
There's both precedence in both directions.
1. The Stellar mode section says "some of your revelations are X aligned and become more powerful while attuned." This leads you to believe that if a power has "while attuned or fully attuned" that it is referring to that specific mode, but...
2. Looking at the revelations, only a few explicitly state a specific attunement - most just say "while attuned or fully attuned" but we have the precedence set by Black Hole/Supernova and other zeniths that it will explicitly call out which attunement when you must be attuned to a specific mode.
So its really a question of which it is meant to be, and there's evidence in both realms to argue for it. If its meant to be left up to GM interpretation, that'd be a nice callout :)
Some powers say you have to be in either photon or gravity mode, others don’t. You just have to read the power to make sure you which it is. Both options are valid depending on the power.Some powers will work even without being attuned at all. For example Flare. When you become attuned, it becomes better.