Fullbright forces your client to render every block as if it is at a light level of 15. Caves, ravines, the Nether, and nighttime overworld surfaces become as bright as a sunny day at noon.
"The mod crashes on launch." Solution: You likely have an outdated Forge version. Reinstall Forge 1.12.2 (recommended version: 14.23.5.2860). Also, check that the mod is specifically for 1.12.2, not 1.12 or 1.12.1. fullbright 1.12.2 mod
Download Fullbright for 1.12.2 from CurseForge today, install it via Forge, and never fear the deep caves again. Have you used the Fullbright mod on a server and gotten banned? Or do you swear by it for mining efficiency? Share your experience in the comments below! Fullbright forces your client to render every block