Thermal or infrared energy is light that is invisible because the wave length is too long for the human eye and forms the part of the electromagnet spectrum that we experience as heat. Contrary to visible light, everything with a temperature above absolute zero radiates heat in the infrared world. This is the source of our heat.
Infrared heating or radiated heat works just like nature: Each day heat waves originating from the sun reach the walls of your house for example. The walls in turn store the heat that is then very slowly released. In the evening the ambient air cools down but you can still feel the heat coming from the walls. A hot stone massage for example, works on the same principle.
An important feature of infra-red energy is that it had a yield of 100%, so that all the heat produced also ends up where it should be. There are no chimneys or piping to allow energy to escape.
Because convected heat warms up the air and starts circulating it also stays longer in the room. Warm air rises so that the heat at the ceiling is significantly warmer than at the floor. Consequence: cold feet and a warm head. With radiated heat the warmth is released directly into the room and is more evenly distributed and can be appreciated sooner.