Dark brown sugar vs. Light brown sugar

I use light brown but I wouldn't say it's the only one you can use- dark brown can most definitely be substituted to get the caramelly undertones that everyone here is talking about. In the end it's all about personal preference! They are interchangable from my experience from a baking point of view.

I have a definite preference for the taste and texture of the dark brown. Unless a recipe specifically calls for light, and I can tell that using dark will compromise the results, I'll go with the dark every time. I'm a huge fan of the butterscotchy undertones it creates that I just don't find with light brown.

I think you'll be fine. Add a splash of molasses and a pinch of baking soda if you're worried. And now back to important issues: the Mavs are 3 and 1 against the Heat!

See, I knew about the molasses bit...but I guess I get a bit confused when a recipe calls for equal amounts of both.
I have the Joann Chang book "Flour" and she swears by using only light brown sugar. Since I've made some of her goodies, that's what I stuck to-but I found a recipe a few days back that called for equal portions of both dark and light.
I really like a moist cookie though. I just want to be sure if I use all light it won't be too dry I guess?

It's all a science experiment!

I'm with boulangere on using whatever I have on hand. The only time I'm really picky about using one or the other is with cake (mainly because of flavor), but even then I'll fudge it unless I'm making it for a customer. I'm also known for increasing the amount of brown sugar or using all brown sugar on purpose because I adore the flavor of molasses.

I rarely bake recipes that are too particular and I've subbed in light for dark without changing any liquid. In a particular recipe, I guess I'd add a little molasses to my light brown sugar. Glad to know boulangere's trick for adding baking soda to sub in the reverse!

I probably shouldn't admit this here, but when I bake at home, I use whatever I have on hand. If it's dark and a recipe calls for light, I'll add an extra pinch of baking soda to compensate for the additional acidic molasses. Is the result a bit different? Perhaps, but it's never been anything I couldn't live with. Worry about who's going to win the NBA championship (go Mavs!), not the color of your sugar.

the difference is the amount of molasses. dark has more, light has less. if your recipe is calling for dark and you only use light, your product will probably not be as moist or flavorful as it should be, depending on what you're making.