Radiant energy © Siemens Stiftung 2017 CC BY-SA 4.0 international

Radiant energy


Formulae for the radiant energy of electromagnetic waves and Planck's law of radiation.

English, Spanish (CREA), German
Image (154.0 kByte)
Radiant energy is the energy of electromagnetic waves. It is proportional to the square of the amplitude of the electrical or magnetic field strength. Electromagnetic waves of high frequency and therefore high energy have the character of particles. The energy of these particles is proportional to the frequency and inversely proportional to their wavelength. The proportionality factor is Planck’s quantum of action h. Max Planck discovered in his investigation of radiation from black bodies that radiation energy must be composed of discrete quanta. He formulated a law of radiation which could not, however, be explained until Einstein postulated light quanta.

Numerical example of Planck’s radiation formula:
The sun has a surface temperature of 5,800 K; the associated radiant power according to Planck’s radiation formula is 3.85 x 1023 kW. Only a very small proportion of this strikes the earth (with vertical radiation incidence 1.37 kW/m²).

Information and ideas:
Radiant energy can be converted into other energy forms. In the case of an X-ray radiograph the radiant energy is converted into chemical energy (blackening of the photo film), light is converted into electrical energy in a solar cell, and similarly radio waves in an antenna. The energy of microwaves can be used for heating food.
There are no other media directly related to this file.
Physics; Technology
Grade 10 to 13
Middle/high school; Vocational training
Chart; Energy; Optics; Power generation; Power plant; Renewable energy; Solar energy; Solar technology; Wave (physics); Energy source; Form of energy; Graphics; Photovoltaics; Renewable energy; Solar cell; Solar energy; Solar power plant; Source of energy; Wave optics
Siemens Stiftung Media Portal
MediaHouse GmbH
© Siemens Stiftung 2017
Stay up-to-date!

About four times a year, we inform you about new media on this portal as well as current studies and events related to OER and STEM.

Media Portal newsletter – register now

About four times a year, we inform you about new media on this portal as well as current studies and events related to OER and STEM.

*Required fields


Liebe Nutzerin, lieber Nutzer,
El Portal de Medios – das spanische Medienportal – ist umgezogen und heißt nun CREA.
Auf CREA finden Sie weiterhin hochwertige Medien für den MINT-Unterricht und vieles mehr.

Dear User,
El Portal de Medios - the Spanish Media Portal - has moved and is now called CREA.
On CREA, you will continue to find high-quality media for STEM education and much more.

Estimado usuario, estimada usuaria,
El Portal de Medios – en español – ha sido trasladado y ahora se llama CREA.
En CREA seguirá encontrando medios de alta calidad para la enseñanza de STEM, y mucho más.

Zu CREA wechseln / Switch to CREA / Cambiar a CREA
CREA - El Portal de Medios para la Enseñanza STEM

Hierbleiben / Stay here / Quédate aquí:
Fenster schließen / Close window / Cerrar ventana