A nanothermocouple detector includes a nanowire coupled across two electrodes. The two electrodes are electrically connected to an amplifier. The two electrodes generally have a separation of about five micrometers to about thirty micrometers across which the nanowire is coupled. A focusing element is disposed to admit photons that fall on the focusing element onto the nanowire to heat it. A voltage change across the nanowire caused by the heating of the nanowire by the light is detected by the amplifier. The voltage change corresponds to the energy absorbed from the light by the nanowire. The color of a single photon can be detected using such device. An array of such devices can be used for sensing light on a two-dimensional scale, thereby providing an image showing small variances in the energies of the light impinging upon the detector array.