there are two types of break lights
there are some break pads for V break that have a LED in them that reacts to pressure, the downside is you have to sick with the rubber (hehe I can say that i am not english speaking
) goes along
I have seen in a chineese marked on a trip in Budapest once break light system, that had a large back light, and also turning signals, that you could operate form a sitch that you mont on the front bar.. teh brake light funktion worked with a sensor on the break cable, it looked and was realy cheap (5$)
personally I don't think this is usefull but I hoped that answerd your question..