CurseForge is the safest and most prominent repository for Minecraft modifications. Many creators upload simple light-map adjustments under the "Resource Packs" category. Search for "FullBright" and filter the game version dropdown menu specifically to . 2. Planet Minecraft
Ensure the Fullbright pack is placed at the very top of your selected resource packs list so it overrides any other packs you are running simultaneously. fullbright texture pack 1122 link