An update to my question: in a standard car, when one takes one's foot off the brake, the car immediately begins to slow down, but there is no indication of this relative to the brake lights (something I have always thought as illogical: since the car slows down, doesn't it make sense to tell the driver of a car behind you that it is doing so with a yellow light, or something?), and then the brake light only comes on when one applies the brake.
In a Tesla, the car also begins to slow down immediately with regenerative braking, but more dramatically, of course. I have observed that the brake lights on the avatar come on at some point, but don't seem to do so immediately. So, if that is the case, my question is: at what point do the brake lights come on: as soon as the pressure on the accelerator is eased, or when the foot is completely removed from the accelerator, or at some point after the car has slowed down to some percentage of its original speed, or what?