Dramatic lighting is awesome for setting a scene and drawing attention to important details. But similarly, it can also be used to draw attention away from important things that you'd rather the heroes overlook.
Have a handy shaft of light fall directly onto the impressive looking sword resting on the unholy altar, but the equally important evil frog-god statuette is lurking in the shadows in a dark corner of the room.
Commentary by memnarch (who has not seen the movie)
And yeah, when you think about it, the light shining in would have to be just for the dramatic flair. Bright light like that from the nearby star wouldn't be able to cut through the fog outside just on its own. Especially when it's also got to cut through the fog or dust or whatever is scattering the light in that beam as well.
A very interesting setting to say the least. Excluding the light, the inside here is obviously focused on the relics with the way the wood is sort of spiraling out from it. Luke obviously would know about this place, having lived here for a long-enough-to-water-rot-an-X-wing length of time. So would this have been something he'd set up, maybe with Lor San's help? Or something he'd found and decided to use?
Hm. Or maybe something to protect. I'm not sure what would be worth protecting here that would need to stay here, but that's an idea I hadn't considered yet. I'm not sure it would fit all of the scenes prior, but I think that concept could possibly fit in a Star Wars movie. There'd have to be a reason why Luke didn't look like he'd wanted company, but protecting something would also be an additional reason for Rey to stick around on the island besides trying to become trained. Assuming Chewie and Artoo haven't just left with the Falcon as well.
GM: You don’t sense any danger, but do feel... restrained power. Like a tightly wound spring.
Rey: I approach the opening and look inside.
GM: The interior of the tree is spacious.
GM: A single shaft of light falls on a small shelf. It contains a dozen or so ancient relics.
GM: Rectangles a few centimetres thick, arranged vertically next to one another, strange sigils on the leathery edges facing you.
GM: The foliation you feel is focused here.
Rey: The light just happens to land there? That’s the sort of thing that happens at midday on the summer solstice, not just randomly.
GM: It’s... a consequence of the Force warping the light rays.
Rey: It makes a special effect just to look dramatic?
GM: Mysterious are the ways of the Force.