Every webcam could be different, but, from everyone I have seen, the light is not controllable/accessible from the operating system - it is simply activated/deactivated on the webcam itself when the webcam is in use.
Based on this, not saying it is impossible, but, it is impossible on every laptop I have seen.
update:
Recent security attacks against Apple cameras on laptops show it is possible to reflash the firmware and disable the light on the camera.
Again, this is very dependent on hardware - if the light is activated inline with the camera, it won't be possible to deactivate. If like Apple, the light is just turned on/off as part of an unrelated firmware command, you will be able to patch it out.
Related over on Security.SE site: Can webcams be turned on without the indicator light?
– Ƭᴇcʜιᴇ007 – 2014-10-30T15:59:49.637