Lighting Design Glossary

Radiant Energy

(Term of radiometry)

The energy transported by electromagnetic radiation. When this radiation hits an object in its path, then it may get absorbed partly or completely and transformed into some other form. For example, this is the case with the microwave radiation (electromagnetic ration near ca. 5 GHz) when it is absorbed by the water in your food, and transformed into thermal energy (heat).

The special case we are interested in is of course the energy transported by electromagnetic radiation within the spectral band visible to the human eye. We usually measure the output of a light source in radiant energy weighted by the spectral response curve of the human eye per time unit, its luminous flux.

Standard unit for radiant energy is Joule (j).