hardcore dark is a mod designed to increase the difficulty of your Minecraft games, making the darkness of the game practically complete. This way the mod removes sky lighting and greatly reduces the illumination range of any light emitting blocks or objects.
As you know nowadays even in the darkest places in Minecraft like caves players can manage to walk without torches because although it is a dark place there is a lighting that allows us to see more or less where we are going. This mod is responsible for complicating our lives, making darkness really a problem if we do not have light sources, and even having them.