![]() An appropriate detector of cross-sectional area 1 m 2 is pointed directly at the source of the radiation.In this case, spectral flux density is the quantity that describes the rate at which energy transferred by electromagnetic radiation is received from that unresolved point source, per unit receiving area facing the source, per unit wavelength range.Īt any given wavelength λ, the spectral flux density, F λ, can be determined by the following procedure: Characterizing an artificial collimated electromagnetic radiative beam.įlux density received from an unresolvable "point source" įor the flux density received from a remote unresolvable "point source", the measuring instrument, usually telescopic, though not able to resolve any detail of the source itself, must be able to optically resolve enough details of the sky around the point source, so as to record radiation coming from it only, uncontaminated by radiation from other sources.Characterizing a natural electromagnetic radiative field at a point, measured there with an instrument that collects radiation from a whole sphere or hemisphere of remote sources.Characterizing remote telescopically unresolved sources such as stars, observed from a specified observation point such as an observatory on earth.The terms used to describe spectral flux density vary between fields, sometimes including adjectives such as "electromagnetic" or "radiative", and sometimes dropping the word "density". The terms irradiance, radiant exitance, radiant emittance, and radiosity are closely related to spectral flux density. ![]() In SI units it is measured in W m −3, although it can be more practical to use W m −2 nm −1 (1 W m −2 nm −1 = 1 GW m −3 = 1 W mm −3) or W m −2 μm −1 (1 W m −2 μm −1 = 1 MW m −3), and respectively by W It is a radiometric rather than a photometric measure. ![]() In spectroscopy, spectral flux density is the quantity that describes the rate at which energy is transferred by electromagnetic radiation through a real or virtual surface, per unit surface area and per unit wavelength (or, equivalently, per unit frequency). Quantity that describes the rate at which energy is transferred by electromagnetic radiation
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