White light coming from ground

I don’t know why I have this unusual white light coming upwards from the ground in a supposedly fully dark room.

I have tried messing with my directional light, exponencial height fog and sky sphere but without any luck.
Can anyone help me please?

I’m sorry, but I do not understand your answer. I don’t have any light source pointing up, that’s my problem

that will also do the job for directional light and skylight

I’m sorry for being away for so long without a reply. As I said before, that is not the problem. Disabling any of the three components I stated before do not change the outcome.