Originally Posted by shambhukumar

i think it will work...
why does LED lamp glow.it is because in BJT base is forward biased with respect to emitter.so current goes from collector to emitter. if we make base -emitter reversed biased then there will be no current from collector to emitter and LED will not glow.
just apply some voltage at base of BJT to make initially LED on.now connect the emitter with the sensor (heat sensor) output.i.e voltage produced by the heat sensor.initially LED will be glowing. when there will be too much heat then sensor voltage will increase and at some time it will be more than base voltage. at that situation base emitter will be reversed biased and there will be no more current coming from collector to emitter. thus LED will be off. i hope it will work.if you want to stick to BJT.