infrared:  Light, radio and infrared radiation are forms of energy.  This type of radiation takes the form of waves.  Radio waves have very low energy and a long wavelength.  Infrared waves have more energy and a shorter wavelength.  Radiation with even  more energy and a shorter wavelength is called light.  Infrared radiation is produced by hot objects.  Cooler objects emit less infrared radiation than hotter objects.  Infrared photography detects the amount of heat emitted by an object. Infrared radiation is invisible without special instruments.  The word infrared means "below red."  It refers to infrared