A/C on in cold weather

Why does my air conditioning light come on during cold weather. Does this have someting to do with "reverse a/c" or humidity?

Two reasons: Dehumidify to prevent fogging and to circulate lubricant through the A/C system in an effort to maximize system life.

So it does not use "reverse A/C" to generate heat for the car?

Not that I'm aware of. That would be a heat pump and would require a reversing valve. I've never run across a reversing valve in the LS (or any other car)...

Thank you CGGorman.