Specifically for 1.12.2, creators often utilize specific file structures (like lightmap.png ) to override how the client renders darkness.
For single-player use, it is simply a preference. However, many competitive servers ban the use of "X-Ray" packs. While Fullbright is technically different from X-Ray (which makes stone transparent), some server anti-cheat plugins flag it as an unfair advantage. Always check server rules before using it in multiplayer.
This forces Minecraft to ignore the brightness cap entirely. It is actually more effective than most texture packs for 1.12.2. However, be warned: This makes the game incredibly bright. Looking at snow biomes will feel like staring at the sun.
This is a hot topic in the 1.12.2 community. Where do you draw the line?