[Help]Light setting issue, why my wall lightness is different?

I tried to build a dark room for testing, during the building I found these things happening:

with a geometry box brush and Light checked, it look like this.

with a geometry box brush and Light unchecked, it look like this.

I build a same box with cube, light checked or unchecked, it look like this.

I haven’t place any lights inside the box btw.

Where is the light coming from? Why the floor always darker and ceiling always lighter, and why in pic 2 the light pass the ceiling and light the floor, it should be a black box since I didn’t place any lights in, right?

Did I miss anything? Pls help, thx.

It can be auto exposure on the camera.