My iSight camera turns on automatically

When I turn on my computer my iSight camera turns on automatically and stays on, even when I put my laptop to sleep. I have a number of programs open, but none that require the camera (FaceTime, Photo Booth, etc.) I don't want to disable it because I do use FaceTime occasionally, but I don't want it to turn on unless I need it because it wastes battery. How can I turn it off the iSight camera when I'm not using it?

Thanks