A large part of that would depend on the type of site you use. There are scripts and such that might be able to turn the light off, I have read about a few. But you have to give those scripts/ apps access in the first place by installing them on the computer.
FLASH chat asks for the use of your cam and mic. Go to the Adobe site and go through their guide for settings.
http://www.macromedia.com/support/documentation/en/flashplayer/help/index.html
The safest way is not to use. Next, is to learn and clear out all the permissions after each session, even though you will see names of things you did not recall giving permission to.
I have used SKYPE, and found that I have a problem reclaiming my cam and mic for apps like iMOVIE. I also found that FLASH seems to give my access to sites I was not on. So I found it best to stay away unless I wanted to clean up after each use. THIS has just been my personal feeling about them. If you want to use that things, you have to clean up. At the very least that will clutter the system down with traffic on your open ports. So I have found.
Did that help?