I just had troubles with Ender IO powered spawners, that stopped working in my mob farm.
After several tries and the help of a few people we figured, that the flood lights were preventing the spawners from work.
However I tried to turn the flood lights off and have the spawners work in the dark. Nothing changed.

I had to change the immersive engineering config floodlight_spawnPrevent to make them work again.
So the floodlights prevent spawning by pure presence?
If I now deactivate this in the config, they will still prevent spawning due to light levels, right?

Would be nice to know how this works.

The fake light blocks generated by the floodlight (in the direction it's facing) as well as the floodlight itself prevent spawns in a 32 block radius

So the fake light blocks will only block when the floodlight is activated? And the floodlight itself will block always in its 32 block radius?

When I put a false in the floodlight_spawnPrevent, then this behaviour is deactivated and only the light levels work on spawning?

Yup, that should be about it.