The smallest energy for photons is in the range of the infrared radiation. Longer wavelengths are related to modulated EM radiation called radio waves and micro waves.
Is the above statement correct? What the spectrum of these photons looks like and depends on? Does it change if the emitter is cooled (to near 0K perhaps) or heated? Can we measure those individual photons to say something about the emitter (and/or the reflector) that we cannot say based on the radio wave as a whole?
A popular answer, suitable for anyone with engineering background, is preferable.