When a recipe calls for “brown sugar,” what should you use? Generally it means light brown sugar should be used. In a pinch, dark brown sugar can be substituted for light brown; however, when baking recipes sensitive to moisture and density (such as cakes) the difference in moisture content can affect how well the cake rises. Swapping the two will also affect the recipe’s taste and color. Dark brown sugar has a deeper molasses flavor, and of course, a deeper color.