Set up a simple light source
Inside the room x=0...6,z=0...8 place four regular lanterns at level y=1: (1,1),(5,1),(1,7),(5,7) x,z. The floor is at y=0, the main passage passes through x=2…4. This is the author's starting layout for a room without partitions, and not a guarantee of any interior.
Check out the entrance, work blocks and stairs at night without shader and night vision effects. Lamps near the walls should not go down into the doorway or cover the head on the stairs.
Check block light after partitions
In official release Java1.18, zero block light is listed as a condition for normal natural spawning of monsters. Do not extend this to spawner, slime and all Nether creatures. On the server, conditions can also be changed by plugins.
In Java, use the available lighting display in debugging information or your version's proven tool. Check the level at the surface, not the brightness of the picture. After installing a cabinet, beam or wall, re-inspect the corner behind it: the previous open layout has already changed.
Look for the specific source of the problem
Walk around the living floor, upper shelves, attic, outside ledge and garden. Mark dark accessible surfaces and add a local source there. Separately, go outside the base and return: the light should show the door and the turn.
If the mob still appears, find out whether it came from outside, fell from the roof, or appeared due to special mechanics. Another flashlight will not replace the door, fence or spawner check. Choose the decorative color of the light after eliminating these reasons.
Hangers and beams should not reduce the clearance of the stairs. Match the light to the height of the passage.
The underwater effect helps you see, but is not a substitute for checking surface conditions. Don't confuse visibility with lighting.
