Toning exercises are done to teach the body to more efficiently conserve it's resources (such as oxygen) and to build endurance. Doing that many reps with that light of weights is likely not achieving much of an effect at all. Your muscles are developed by use, and that easy of an exercise relates closer to cardio than to a true workout.
Simply put, there are two types of muscle tone: myogenic and neurogenic. The former refers to your muscle tone at rest; the latter refers to muscle tone that's expressed when muscular contractions occur.
Low(er) rep training increases the sensitivity of various motor units resulting in increased neurogenic tone. On the other hand, myogenic tone is correlated with the overall density of your muscles (specifically the contractile proteins myosin and actin) and is vastly improved by lifting heavier weights. (Source)
So, yes, you can do more reps with lighter weights to make your muscles look better in a relaxed state, and less reps with heavier weights to make them look better in a contracted state. As a general rule, I've always been told to use the maximum weight you can do 12 reps with for toning, and the maximum weight you can do 7 reps with for building. The same article I've quoted there also says:
"... utilizing light weights (anything above twelve reps in my book) while dieting will likely result in loss of muscle, which is the exact opposite of what you want to happen."