Copper bulbs always generate completely unoxidized in the geyser/fountain room of trial chambers. This makes the room much more lit than other chamber rooms when encountering it.
To reproduce, use the seed 6692886807253187318 and run the following commands, noticing that all of these rooms are unusually well lit:
/execute in minecraft:overworld run tp @s 2193 -8 -801/execute in minecraft:overworld run tp @s 6791 -30 -980/execute in minecraft:overworld run tp @s 6804 -12 -2441
All rooms have a mix of oxidised and unoxidised copper bulbs. Even in the fountain room you can spot some oxidised bulbs. This is likely an intended feature.