Irradiance of a surface per unit frequency or wavelength. This is sometimes also confusingly called "intensity". Radiant flux received by a surface per unit area. Watt per steradian per square metre, per metre This is sometimes also confusingly called "spectral intensity". The latter is commonly measured in W⋅sr −1⋅m −2⋅nm −1. Radiance of a surface per unit frequency or wavelength. Watt per steradian per square metre per hertz Radiant flux emitted, reflected, transmitted or received by a surface, per unit solid angle per unit projected area. The latter is commonly measured in W⋅sr −1⋅nm −1. Radiant intensity per unit frequency or wavelength. Radiant flux emitted, reflected, transmitted or received, per unit solid angle. The latter is commonly measured in W⋅nm −1. Radiant flux per unit frequency or wavelength. This is sometimes also called "radiant power", and called luminosity in Astronomy. Radiant energy emitted, reflected, transmitted or received, per unit time. Radiant energy detectors produce responses to incident radiant energy either as an increase or decrease in electric potential or current flow or some other perceivable change, such as exposure of photographic film.
Many of these applications involve a source of radiant energy and a detector that responds to that radiation and provides a signal representing some characteristic of the radiation. These include treatment and inspection, separating and sorting, medium of control, and medium of communication. Various other applications of radiant energy have been devised. Because of this, the air temperature may be lower than in a conventionally heated building, even though the room appears just as comfortable. The heat energy is emitted from a warm element (floor, wall, overhead panel) and warms people and other objects in rooms rather than directly heating the air. It can be generated electrically by infrared lamps, or can be absorbed from sunlight and used to heat water. Radiant energy is used for radiant heating. Radiant energy is produced in the sun as a result of nuclear fusion. The absorbed solar energy is partly re-emitted as longer wavelength radiation (chiefly infrared radiation), some of which is absorbed by the atmospheric greenhouse gases. In geophysics, most atmospheric gases, including the greenhouse gases, allow the Sun's short-wavelength radiant energy to pass through to the Earth's surface, heating the ground and oceans. Such a system can be man-made, such as a solar energy collector, or natural, such as the Earth's atmosphere. Radiant energy is one of the mechanisms by which energy can enter or leave an open system. EM waves can also be reflected or scattered, in which case their energy is redirected or redistributed as well.
Often this phenomenon is associated particularly with infrared radiation, but any kind of electromagnetic radiation will warm an object that absorbs it. This is a very familiar effect, since sunlight warms surfaces that it irradiates. When EM waves are absorbed by an object, the energy of the waves is converted to heat (or converted to electricity in case of a photoelectric material). This implies that if two EM waves have the same intensity, but different frequencies, the one with the higher frequency "contains" fewer photons, since each photon is more energetic. In the wave picture, the energy of a monochromatic wave is proportional to its intensity. In the particle picture, the energy carried by each photon is proportional to its frequency. 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. ĮM radiation can have various frequencies. These two views are completely equivalent and are reconciled to one another in quantum field theory (see wave-particle duality). Alternatively, EM radiation can be viewed as an electromagnetic wave, which carries energy in its oscillating electric and magnetic fields. Cherenkov radiation glowing in the core of a TRIGA reactor.īecause electromagnetic (EM) radiation can be conceptualized as a stream of photons, radiant energy can be viewed as photon energy – the energy carried by these photons.
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