effects
Sets the effects
property of this DimensionType, which determines the ambient effects the client will display in levels of this DimensionType. These are hardcoded client-side so only the vanilla values can be used:
BuiltinDimensionTypes.OVERWORLD_EFFECTS
BuiltinDimensionTypes.NETHER_EFFECTS
BuiltinDimensionTypes.END_EFFECTS
For a deeper understanding of what these values do, check out the Minecraft Wiki (effects property).