Light has different types of radiation, some of which are visible to the human eye and others which are not. One of the types of radiation emitted is visible light which is, of course, visible to the human eye. On the radiation scale, visible light is between ultraviolet light and infrared light.
Ultraviolet light has more energy than visible light, but is not perceived by the senses. On the other hand, energy emitted by infrared light is perceived as heat. This energy is felt, for example, when sun shines through glass and the skin heats up, even if this protects from ultraviolet rays. Thus, complete light radiation always contains these types of radiation, but in different proportions. What do these proportions depend on? Dr Puig explains.