Hi, chef, this type of question is better asked in the Cooking Q&A forum.
There are substitutions in a number of places. Cooking Q&A has a sticky with substitutions near the top of the forum,
http://www.food.com/bb/viewforum.zsp?f=2&sid=f1074357cac4bcf9f98d6c9f79cdf483
The Kitchen Info forum has also collected various tips, including subsitutions here,
http://www.food.com/bb/viewtopic.zsp?t=374223
The Great Britain and Aussie forums have substitution lists for ingredients from other countries.
For baking ingredients, I often go to this site,
http://baking911.com/learn/substitutes
Here is info about brown sugar
1 cup light brown sugar, packed = 1 cup dark brown sugar, packed = 1 cup granulated white sugar; or,
1 cup granulated sugar + 1/4 cup light molasses
1 cup dark brown sugar, packed = 1 cup light brown sugar, packed = 1 cup granulated white sugar; or,
1 cup granulated sugar plus 1/2 cup light molasses or 1/4 cup dark molasses