Webcams and other digital video recorders are sensitive to light, just like cameras. In general, you do not want light fixtures directly in the view of the video recorder. Try setting up your video so that the video recorder has his back to any bright light fixtures in the room, just like you would take an outside photograph with your back to the sun.
If you find that your video is too dark, try adding an extra lamp to the room. Be sure that the lamp is not in direct view of the camera. If you can, try placing the lamp just behind the camera, but aimed towards the general area that you are recording. (Important: Don’t blind yourself in the process by staring directly at a bright lightbulb while recording your assignment!) You can also switch to a brighter room or try recording your video at a different time of day when there is more light outside that can shine through a window.