I had this same issue in one of my magic farm worlds. Angry zombies *never* spawned anywhere. I ended up making a dark room around a sinister node. A sinister node will convert the biome around it in (I think) a 9 block radius. If it is dark, sinister nodes will spawn angry furious zombies. (This is separate from the normal spawning mechanics.) That was my only source of zombie brains on that map.
Hopefully you can find a sinister node an move it some place convenient for you and make a dark room around it.
Edit: I forgot that the nodes spawn furious zombies and not angry zombies, but both drop brains, so I had what I needed.
This is what I ended up making for magical spawns. I found a magical forest biome, outlined it, then filled it in. Got pechs soon enough to trade with to get my greatwood and silverwood saplings. Later, when looking for angry zombies, I ended up expanding it out (grass/bone brick area) into a Jungle biome. Also spawns ocelots then too, whee! But once I expanded out, plus removed all light, I've had both pechs and angry zombies spawning with regularity at night. Other stuff too obviously, but I just ignore or kill it all.
Here's the tower. Can you tell from the picture which lamps are lit?
Agreed. Did some tests myself, with the available illumination options.
Night
Day
As the road lights have an obvious yellow "lamp" in them, they might be good options too. I agree that the Illuminators are hard to tell apart, especially with different colors. But with one color (redstone lamps/road) you don't get the pretty effect like with the Neon lamps. Just put the cable to the side, not behind, as otherwise you can see it through the lamp. They won't be hard to get to, once you let the fishing nets run for a while. Just make some plastic using the ethanol recipie, and there ya go.
Danko. Without looking at the pics, is your Infusion Altar? fully stabilized? I guess I should have mentioned that in my ask [old age]. Space isn't an issue. I've got 100+ blocks in x/z to play with before I have to tack on another chunkloader. I'm trying not to build so cramped this time...but old habits die hard.
I'm just throwing out ideas for you while I think about [drag my feet] how I want to setup my mob farm/collection area/Blood Altar/ and where to put my Idiots [villagers].
If I keep my Idiot spawn zone 32+ blocks away from their sacrifice area, can I still trade with them [is there even a point]?
Can't see the bottom of his, but here's the bottom of mine. Not symmetrical due to how heads can be placed on a "wall", as I started the front too far back, I couldn't add the 2 more rows without redoing it all. I was able to craft all the staff cores (thinking I needed the
staff cores for the primal staff, not realizing it's merely
wand cores and
staff research), then the staff core of the primal, with no instability I could tell of. Haven't lost an item except once when I forgot to have an aspect ready first. Runic matrix is above the one with my crosshairs.
Also, bonus pics. You mention your idiot spawn and sacrifice area. For ongoing LP filling, consider a witch room. As pictured below, I have my original conveyor-belted villager spawning area for quick fills if necessary, but also a 51 witch jail right on top of my well of suffering. Probably overkill, especially as I haven't lost one yet thanks to their drinking problem, but it gets me plenty of LP to make a constant supply of slates, sockets, or keep my orbs filled. With 14 runes of sacrifice and 34 speed runs, it'll run continuously making Demonic Slates, topping up in the middle of each one. 1200LP to the altar per "hit" of the well. Actually just tested, and it'll fill blood sockets too without villager sacrifice. They run the altar dry, and I see grey sparkles, but after ~20secs, I still end up with a filled socket. Guess I don't need my villager auto-spawner anymore!