Because of the small amount of molasses in light brown sugar, it will caramelize easily in the oven when cooked on the bacon, giving you a sweet flavor and perfect texture. If you use a different kind of sugar, you will not get the same caramelized coating. That being said, if you have to use a replacement, stay away from granulated sugar and stick to dark brown sugar or any coarse sugar. This will give you a slightly sweeter flavor and the closest results to using light brown sugar.