Screen Dimmins Help

Hey, I have a 15 inch aluminum macbook pro, Snow Leopard and recent updates all installed, but i noticed something on my friends 13 inch macbook pro that mine doesn't do.
On my friends, when you press the screen dim/bright button (F1, F2), its a gradual transistion, but on mine it just jumps down a notch.
For example, when you hold down the dim button on my friends MBP, it the screen dims in a similar way as to when you put your finger over the iSight camera, it fades to a dimmer screen. On mine, it jumps down each brightness level
Any help would be appreciated, thanks