This mod provides users with a NEI-like light overlay.
Light Overlay is a client ONLY mod, putting this on a server will do nothing.
Press F7 to toggle the light overlay, configurable through Controls Settings.
A yellow cross means that mobs can spawn at night, a red cross means that mobs can spawn anytime.
This mod does not work well with OptiFine shaders: https://github.com/shedaniel/LightOverlay-Fabric/issues/5, however you can use the number display mode which will work with shaders.