Fully bright in low light levels

In areas where the sky is not overhead, and even in areas completely boxed in with solid blocks (dirt, stone etc) it seems like it is at level 15 brightness, despite being at a lower brightness in the F3 menu.

The attached image is my character in survival, completely boxed in with solid blocks at level 0 light from block or sky. I tried placing torches to "reset" the light, but that did nothing. This is also not the first snapshot with this issue, but I am unsure which snapshot I was playing when I first encountered this.