Wrong. Where did you get that from?
"The real story is that our lady Tyrande Whisperwind has had visions of a great light we would... will... find on this journey. A light that will need to be found and defended."
aka the Vale.
She says that Tyrande sent them as a vanguard for the Light. Capital-L Light.
Neilson recently just said that while Tauren Sunwalkers use teh light, they are taking a different path to get to the same source.
Elunites powers on the other hand, he said come straight from Elune. So them using the light is unlikely.
But yes, the constant "Night Elf/Light" crap is bugging me.
I overlooked the Night Elf priests in Cata chilling with the Argent Dawn and using light based spells like the seeing through they eyes one, because meh, game mechanics.
But I think The Light the sentinel was referencing was the vision Tyrande had.
Which fits perfectly with the definition. The Sentinels in Northrend were the vanguard for the light Tyrande saw. They are leading the way into a new phase of life that they believe will grant them immortality again.
Tyrande's voice carries a lot of weight, and it's not all that farfetched that they took on that belief when they brought with them a guy raging abotu getting back immortality.