The world below is not without color, the fog shrouded as long as there is light can still see some color, but these light shining on the body does not seem to have any temperature.
The light source itself is actually alive, they are the output of some half-plants and half-biology underground, also like symbiosis, no one can figure out why. Just remember that if you feel hungry near these lights, the body will slowly replenish energy.
Those creatures seen yesterday collecting these lights may be too greedy, in fact, they also know that as long as out of the cave to the above-ground world, these lights will somehow disappear without a trace.