Usually called a "Gamma Pack" or "Night Vision Pack," a Fullbright pack modifies the game's internal brightness curve. Minecraft usually limits your brightness slider from "Moody" to "Bright." A Fullbright pack bypasses this limit entirely, effectively setting your gamma value to maximum. The result? Caves appear as if they are lit by daylight. Shadows disappear. Black wool looks gray, but you will never walk into a lava pit again because you "couldn't see it."
So, turn down your torch production, stop squinting at your screen, and download a Fullbright pack for 1.12.2 today. The darkness is no longer your enemy. fullbright texture pack 1.12.2
Do not unzip the downloaded file. Simply drag the .zip file into the resourcepacks folder. Usually called a "Gamma Pack" or "Night Vision
Go back to Minecraft. You should see the Fullbright pack appear on the left side of the Resource Packs menu. Hover over it and click the arrow to move it to the right side (Active). Click "Done." Caves appear as if they are lit by daylight