Skylight has the incorrect value at low Y levels.
This Y level can be reached with a custom datapack that has the bedrock very low: customized low bedrock.zip

Reproduction Steps

• Create a world with the attached datapack
• Go into spectator and start flying down
• Observe the skylight value

Observed Results

• The skylight value suddenly becomes 15 at around Y -2048

Expected Result

• Skylight would remain 0