Feature suggestion: Auto Fullbright + Dynamic Brightness Slider

I checked the game difficulty. It was set to Hard.

I walked into a cave I had previously abandoned because it was a labyrinth of unlit corridors. Now, I strolled in like I owned the place. I didn't place a single torch. I felt invincible.

If your Minecraft 1.12.2 still has dark caves after installing a Fullbright pack, check these three issues: