I want to bake a cake but I don't have light brown sugar. Can I replace it with white sugar?
You can make brown sugar from white sugar if you don't have brown sugar on hand. As explained on Cook's Country (paywall):
In the test kitchen, we’ve found that pulsing 1 cup of granulated sugar in the food processor with 1 tablespoon of molasses makes a fine substitute for light brown sugar. For dark brown sugar, use 2 tablespoons of molasses for the same 1 cup of granulated sugar.
THE BOTTOM LINE: Don’t have any brown sugar in the cupboard? Make your own by mixing molasses into white granulated sugar. Or simply add the molasses along with the wet ingredients in your recipe.