Thanks A. Roisch! That was just the info I was looking for. I figured there wasn't much to the 'sensing mechansim' but wanted to make sure. I noticed that if I applied the brake, even somewhat hard, at freeway speeds, the light wouldn't come on at all (I'm assuming from enough airflow to keep them cool), whereas coming to a 'hard' stop at a light, or braking due to an inattentive driver ahead of me, the light would come on bright and constant.
Yeah J. Hidalgo, I did get the new sensors, I've heard they can be replaced but the one's on my 123's were so brittle (or melted) by the time they were due for changing, they didn't come off in one piece