Mike "The Metal Detector" is an almost completely blind sorcerer.
I'm not applying the blind condition, but I impose disadvantage on anything which requires sight, and auto-fail anything which requires seeing detail.
Early in his training, before he was at a level to control it, he ignored his tutor and tried to cast a high level spell which blew up in his face. His eyes are still there but the heat damaged his retinas and he cannot make out any detail, only discern how bright the room is.
What happens if he casts the Darkvision spell (PHB 230) on himself?
Darkvision is always (to my knowledge) used by creatures who also see normal light. So, what would Mike be able to see, for those 8 hours? I can see some possibilities:
Mike can see only the additional spectra of light that a darkvision creature can see relative to a non-darkvision creature, although I'm not sure what this would look like.
It doesn't work at all — darkvision works by upgrading your existing vision functionality and with such badly damaged retinas, the spell fails.
He gains full vision, including the 400–700nm range, and can see as if he was an orc with darkvision.