Human beings give off energy in the infra red spectrum, due to our body heat. Infra red is a spectrum of energy that is just below the lowest frequencies we can see, thus, this light is not visible to the human eye. If we could see infra red light, then when we close our eyes, we would be surrounded by light, far more than what comes to us from the visible light of the world around us. It is there, from us, all the time. We are beings of light. It's just a light we cannot see. Unless we look deeply for it.
Interesting.