Better Brightness Slider expands the default brightness slider, making it range from -100% to 1200% (fullbright) instead of 0% to 100%. It's a clientside mod, so it isn't required on servers. The feature is ported from Boosted Brightness, if you want a fabric version, download it there.
The mod should be compatible with Optifine and Rubidium (Forge Sodium).
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External resources
Project members
LaidBackSloth
Owner
Technical information
License
MIT
Client side
required
Server side
unsupported
Project ID