Radiant energy

The symbol Qe is often used throughout literature to denote radiant energy ("e" for "energetic", to avoid confusion with photometric quantities).

[5][6] For example, the first gravitational waves ever observed were produced by a black hole collision that emitted about 5.3×1047 joules of gravitational-wave energy.

Alternatively, EM radiation can be viewed as an electromagnetic wave, which carries energy in its oscillating electric and magnetic fields.

These two views are completely equivalent and are reconciled to one another in quantum field theory (see wave-particle duality).

The bands of frequency present in a given EM signal may be sharply defined, as is seen in atomic spectra, or may be broad, as in blackbody radiation.

[8][9][10] Such a system can be man-made, such as a solar energy collector, or natural, such as the Earth's atmosphere.

Because of this, the air temperature may be lower than in a conventionally heated building, even though the room appears just as comfortable.