I recently got a Benq LED backlit monitor. Although the picture quality is fantastic, Ive noticed that when the screen goes from white to black a large number of pixels on the right hand side of the screen don't go black instantly. Instead they gradually fade to black (so you can usually see a faint outline of what was on the screen before, when it turns black.)

Is this normal operation for an led backlit monitor or is my one broken

Thanks in advance for any help