Upon further inspection it looked like it was, in fact, lighting up, but very weakly. I'm not used to LEDs being weakly lit. Every one I saw either worked or didn't. So I was puzzled. Fortunately, on the X220 access to the webcam module is very easy - just two screws to remove the LCD front bezel. When I saw what the problem was I almost burst out laughing. Turns out that the last technician who replaced my LCD under warranty used a piece of black mesh tape over the antenna cables in the lid to hold them in place, and cut the tape too long, so that it covered the LED (it is almost indistinguishable at first glance from any other resistor/capacitor, so it's easy to not realize you are covering something that should be exposed).
A trivial fix (and, fortunately, reattaching the LCD bezel on the X220 is even easier than removing it). The fact that it took me over 2 years to realize I had this problem shows you how frequently I use the webcam on my devices, heh.
All is well that ends well.




