Night time sky light remains 15 - no mobs spawn on ground level.

Rather than the sky light going down as it should, it remains 15 at night, causing no mobs to spawn. Even when there are no block lights, the sky light is 15. The sky light only gets lesser when I go into a protected area, such as a cave or under a bunch of blocks. Whilst searching for this bug so as to avoid creating an issue, there were many given answers yet none worked for me, hence why I am making a new one. I have tried increasing the rendering distance which had no effect. Please advise.

NOTE: My computer is being difficult so there are no photos. Basically what is happening is that it is the middle of the night. I have pressed F3, the sky light is 15 and there are no mobs. I'm not sure why I can't get the photos, but I'm trying my best here!!