I have a mod where one of the places added to the game is pitch black. I can see the light on the torches but otherwise there is no light. I tried changing the ambiance values but it didn't make any difference.

This is an interior cell, right? Is the fog density setting for that cell set to 0? You can try setting the fog density to something other than 0, and if that fixes it, then it seems you have a graphics card that has the fog density bug.

http://code.google.com/p/mlox/wiki/Tes3lint can list cells in plugins that have the fogbug.
http://code.google.com/p/mlox/wiki/Tes3cmd can make a patch plugin to fix fogbugs in all your plugins.

More specifically: There is a bug with certain graphics cards that causes the lighting to go wacky when the fog density is set to 0. Setting it to anything higher than 0 (0.01, for example) will allow the lighting to return to normal.

If it's not the fog causing it, then the person who made the light set the light color value to all black. Change it to a more natural color (pick another, similar interior cell and change it to the lighting in that cell).

I already tried changing the lighting color and that didn't work. Thank you John I will try that and see if it works.