Large, enclosed space lit

I was trying to build a mob farm on my server. I built a large, enclosed space, but it was lit by daylight.

What I expected to happen was...:
When I made an enclosed room with no lighting, it would be dark

What actually happened was...:
It was lit by daylight as if there was no roof

Steps to Reproduce:
1. Go on a server
2. Build a large room with no openings or lighting
3. Notice that there is still light