phosphor-fabric VS LambDynamicLights

I remember Notch talking about the lighting calculations being one of the hardest parts to program, so I can understand that being a challenge.

Mojang made large improvements to the lighting engine in 1.20, bringing it in line with the performance mods Phosphor[1] and Starlight[2]. Despite being deprecated now, they might still offer some useful insight into how to approach such a system in a performant way. You'll need to be mindful of the licenses, but it's likely easier than reverse-engineering Minecraft (even with mappings).

[1] https://github.com/CaffeineMC/phosphor-fabric

Phosphor (another optimization mod by the Sodium devs, targeting the built-in lighting system)

Sodium Phosphor Lithium also get iris but I don't have download link

There’s lots of lightweight shader packs designed for low-end PCs. For an optimized, smooth shader experience I’d recommend installing Fabric, Sodium, Lithium, Phosphor, and Iris Shaders.

I would suggest you to use Sodium or Iris - Overall Performance Improvement / Iris If You Wanna Use Shaders Too Lithium - Improve CPU Usage LazyDFU - Launch Game Faster Phosphor - Improve Light Engine Hydrogen - Reduce Memory Usage

Low performance is to be expected with your config. You can try to install these performance mods for minecraft : * Iris that contains Sodium * Sodium, don't use it with iris, it already has sodium. * Lithium * Phosphor

Lithium is only for Fabric. There's also Phosphor to improve lighting performance.

You can get better performance and retain vanilla features by using Fabric with phosphor and lithium.

for newer versions Sodium+Lithium+Phosphor (+aditionally hydrogen)

Lambdynamic lights does that. https://www.curseforge.com/minecraft/mc-mods/lambdynamiclights and it just updated

Pour l'éclairage dynamique, j'utilise LambDynamicLights...

Lambdynamiclights can be used on fabric

LambDynamicLights (by LambdAurora)

LambDynamicLights, hold a light source so you can see

It could be added to pretty much any existing modpack. It's one of those mods that don't really change the balancing of a pack so adding it afterwards isn't won't usually cause issues. You will probably have better luck finding one for forge in 1.12.2 but there is a dynamic lighting mod for the fabric modloader https://www.curseforge.com/minecraft/mc-mods/lambdynamiclights

You could install LambDynamicLights and hold a torch in your offhand.

LambDynamicLights is like the Optifine Torch light (also works with Glowstone and everything that emits light)