Light as a wave will ALWAYS bleed around corners. It doesnt matter how you design it, you cannot create a spotlight that will not give off a small amount of light around the edge. Not that it matters because as we all know, light in the atmosphere even at night leves a bit of a trail due to clouds, atmospheric particles or whatever. it is IMPOSSIBLE for a light source to exist circling above a flat earth that is not partially visible from any location at any time of the day or night.
I've never understood this argument; you can't see a light through a wall. It's not going to curve out around the spotlight, it can only in travel in straight lines from the spotlight. It's easy to design a spotlight that doesn't bleed out around the corners in any meaningful capacity.
I like to imagine it like a cannon. if you put a light bulb within the barrel of a cannon, you're only going to be able to see it from directly underneath; head to the side, all the light from it will still be blotted out. But if you shorten the barrel, sooner or later the light will be visible from more locations than just underneath it.
One thing I'll say is that you do need an obscene amount of delicacy to create a spotlight at the exact level where the collar/barrel blocks enough light that it isn't visible everywhere, but is still visible for long periods of time without distortion. But, honestly, just go with 'God did it' as a placeholder for how the whole system came about, wait for them to get a complete model rather than expecting it to be fully formed.
Whatever light that, say, gets reflected off the air/clouds/whatever is going to be so minimal you wouldn't be able to identify it as the Sun. You'd just get a faint haze, at best, more than likely just not easily visible up against the light caused by stars and the moon.
But to actually be able to see the light source itself supposes a straight-line view from your location on the Earth's surface to the source of the light. A collar or barrel around the light source easily prevents that.