Radiant tube heaters, mounted overhead, produce infra-red radiant heat that is directed downward by a reflector. The primary source of natural radiant energy is the Sun. When standing in the Sun's rays a feeling of warmth is experienced, whilst in the shade it feels considerably cooler. Radiant heat warms all solid objects in its path. Radiant energy is transmitted in the form of electromagnetic vibrations or waves, which are emitted by hot surfaces, travel in straight lines, just like light, and are absorbed by cooler solid objects and surfaces on which they fall. The infra-red heat passes through the air without heating it and falls on people, floors and machinery etc below creating a comfortable all-round radiant warmth at low level.