I considered everything you said when I first wrote this and you are not the first person to say this. I personally believe it's a relic of darkness but there's too much of an open end to be sure. However I couldn't really think of what else so I left it there. :/[spoiler]I first thought golden age experiments with the traveler's light but that leaves a really long stretch on the lighthouse.[/spoiler] I know we are dead but we are not referred to as dead. We are referred to as "the light" by the hive, "Thieves" by the fallen, and "Guardians" by the cabal. We are very rarely referred to as "the dead". The hive on the other hand are very commonly referred to as dead. The ghost even called their fortress a necropolis. The dead [hive] come for these [the machines], but the dead [hive] should not have them. Why? Because they'd almost claim absolute victory, and that'd be bad for everyone. As for the lighthouse. The same effect is not recorded in vertigo or the burning shrine and Shaxx deemed them safe for crucible arenas meaning those effects must not apply everywhere. This leads me to believe it's localised to at least this site.

I believe the Guardians have been referred to as "the dead" in a couple of the grimoire cards, but I could be wrong. The Lighthouse may be a main channel of vex power, while the burning shrine might not be as active. Also, Vertigo is a Cabal base, so maybe since they've overtaken it, it doesn't have as much of an effect?

You are correct. The ghost flower calls us dead and so did Rasputin but he said [quote][long dead, alive again, their bodies grafted to powers they and I do not understand][/quote] Since then, as far as I'm aware, he's referred to us as guardians. Now you'd think if the lighthouse was an important vex function they wouldn't be so ignorant to a cult of guardians setting up shop there and allow guardians to visit week after week. Or at the very least send in a platoon of aphinx invasive to ambush them.