I think I found an issue with the rendering of luminescent blocks:
If you place these at different distances from the player, they look very different from each other. Even if they are just next to each other.
The reason, if I had to guess, is that you assume that light travels only a certain distance. However, that's an inaccurate simplification:
If you stand on an open field, you can see a light-up torch quite far. However, that's different for the surrounding area.
So it makes sense to light surrounding blocks depending on how far they are away from the light source, but not for the light source itself.