Annihilation

I'm pretty sure the shimmer is supposed to represent some kind of cancer or a growing tumor on earth. The doppelgängers are like cancer cells that keep duplicating until they annihilate healthy cells in our bodies, just like how we as people self-destruct. The shimmer is known to reflect light, radio waves, and DNA but it also reflects people's past mistakes and their guilt, consuming them and ultimately making them go mad and self-destruct. The fire in the lighthouse might be referring to lena letting go of a version of herself or maybe it's the surgical procedure to remove a tumor..idk. However, in terms of the ending...I do think the one that got out is the fake Lena. Her eyes were seen glowing at the end and if you pay close attention, you will notice that the water in the cup during the interrogation scene mutate right in front of our eyes. The ending of real Lena being the one to escape the light house might have been false as we see the story from what Lena in the interrogation room tells us. Maybe the fire did catch on the lighthouse but the fake Lena was the one that made it out...who knows