They are interchangeable in talk but let's say you want to build up the "values" on an object, you would add your light and dark values to create the form but you wouldn't say you want to build up the "brightness". The value in a piece almost always refers to the darks and lights in a piece to create form. When someone talks about brightness they are usually describing a specific value such as, how much "brightness" does this color have. That's why it's called an HSB slider. H for Hue, S for Saturation and B for Brightness. I hope this helps =]
