Light corn syrup and dark corn syrup are the two most popular varieties of the corn-based sweetener. They are popular options in a host of American baked goods, confections, and savory dishes because of their ability to resist crystallization and enhance texture. There are some fairly significant differences between light and dark corn syrup, and you will want to take these into account when deciding which to use for a particular application.
How does light corn syrup differ from dark corn syrup?
Light corn syrup is flavored only with vanilla and salt, but dark corn syrup has refiner’s sugar added to it. Refiner’s sugar is a kind of molasses. The different ingredients result in each corn syrup having a different color and flavor. Light corn syrup has a hint of floral vanilla flavor, while dark corn syrup has a caramel flavor similar to that of molasses. Light corn syrup is also a pale yellow liquid, while dark corn syrup has a deep brown color similar to light molasses or soy sauce.
Light Corn Syrup 
Dark Corn Syrup
Can you use light corn syrup as a substitute for dark corn syrup and vice versa?
Light corn syrup can usually work as a substitute for dark corn syrup on its own with no additives; however, it will be a better substitute if you add another ingredient to give your recipe the deep brown color and caramel flavor. For example, you can add molasses to light corn syrup to take the place of the refiner’s sugar in dark corn syrup. Another option that can give you a similar effect is caramel coloring.
Dark corn syrup can work as a substitute for light corn syrup in a few instances, but there are many where it won’t. Because of dark corn syrup’s color and flavor, it may be a superior option to the paler syrup for some baked goods like a pecan pie. It will provide the same sweetness and textural benefits as light corn syrup but will offer a strong caramel note, enhancing the flavor of the pie filling. Before the invention of corn syrup, pecan pie was made with brown sugar to get a similar caramel note. It won’t be a good substitute in light-colored ice cream recipes and recipes for hard candies where the caramel flavor would be out of place.
When should you use light corn syrup, and when should you use dark corn syrup?
Use light corn syrup when all you want is sweetness and a hint of vanilla. Light corn syrup works best when your recipe requires a sweetener with a mostly neutral flavor, and that resists crystallization. Another benefit is that it does not have a significant effect on color. Use it in your light-colored ice creams, sorbets, and candies. Add some maple flavoring to it to make a decent pancake syrup substitute.
Dark corn syrup is the best option when you want the caramel flavor and color. If you need an alternative to molasses that provides a higher degree of sweetness and a milder flavor, light corn syrup might be your best option. Use it in baked goods like pecan pies and chocolate chip cookies. It works in savory dishes as well. Dark corn syrup is excellent as a glaze for ham and gives barbecue sauce extra sweetness and a brilliant sheen.