Picture 1: After the center light turned off, this glow around the lamp on the left appeared.

Picture 2: This wall is solid netherrack. There is nothing behind the light. Nothing powering the light, and very minimal redstone below the floor well outside of the reach of any of the lamps.

Picture 3: upon destroying the lamp on the left, the light vanishes.

This happens every time I light the middle lamp, but it is not always the light on the left that triggers. Sometimes right, and sometimes middle, and it's not always the lamp itself that is lit up afterwards. Sometimes it's  the nether rack behind the slabs. Essentially, any of these blocks act as a pseudo magma block, though they do not maintain the full light level of the lamp in it's lit state, and usually only pick up a light level of (what i'm guessing" is 10, as the light level on the floor where i was standing was 7 and its roughly 3 blocks away.

I can recreate this any time I turn the center light on, but have not tested it with any of the other lamps.

I have tested just powering a lamp with a lamp beside it, on their own, surrounded by bedrock (because that's what my creative world happens to be, so I am assuming is has something to do with the slabs against the wall.