SheBear: I've played the games many, many times. No spoilers will effect me. :D
The BMC mines shouldn't be that dark. I think you should really check your brightness settings.
To equip a lantern put it in the off hand (shield hand) in your inventory. It doesn't make that much light, just a small circle around the PC.
hercufles: I always right that down in case a person reads it and isnt that far. I have checked the setting and its on its brightest as for the dungeon i found a scroll with has teleport out of the dungeon :)
That is very strange that the dungeon is that dark. Have other caves been too dark for you to see well? Places like the silver mine in Shrouded Hills, the Wolf cave near Dernholm, the caves or sewers under Tarant. If it is a general problem then you might just have a dark monitor or you'll just have to actually carry around a lantern on your character. We you able to get to the end of the BMC mines before teleporting out or did you not finish the quest line there yet?
Oh, another suggestion for navigating dark tunnels is to open your map and use the local map to drop way points for your character and move that way if you can't see where you are going in the normal window. I think the map is slightly lighter than the "real world".
Hmm... another thought: I know there is a background that makes the PC able to see in the dark better at the expense of seeing in the light well; is there a similar background which makes you more blind at night/in caves? That could be making it extremely dark.
Also, could you take a screenshot of how dark it is it in the cave? I want to see how dark it is.