An apparatus and method of calibrating a sensor. A voltage is applied to a first carbon nanotube layer to obtain a first temperature of the first carbon nanotube layer. A thermally conductive layer is used to provide a substantially uniform temperature related to the first temperature of the first carbon nanotube layer by smoothing a spatial variation of the first temperature. A second carbon nanotube layer receives the substantially uniform temperature and emits a first blackbody radiation spectrum to calibrate the sensor. The apparatus may be used to emit a second black body radiation spectrum by altering the applied voltage.